The Celestial Tiger's Notes: In this chapter, I'm taking a great deal of creative license to tie both series together with a viable explanation. Please remember that I have only seen Yu Yu Hakusho up to the conclusion of the Dark Tournament saga. If plot or background is given later in the show that contradicts or conflicts with what I'm writing, please understand that I haven't seen that far yet in the show.

P.S. A huge thank you to all of you who like the story and have submitted reviews! It's wonderful to know that it is well-received.

Chapter 4: Lessons on History and Time

The next day, Yusuke, Keiko and Kuwabara were eating lunch together outside on the school roof when Botan flew down to them on her oar. Upon seeing her, Yusuke and Kuwabara's faces lit up and they clambered to their feet in anticipation.

"PLEASE tell me you've got another mission for us!" begged Yusuke. "I'm so frickin bored, it feels like time's going backward!"

Botan smiled somewhat nervously. "Heh heh…funny you should say that, Yusuke."

Yusuke and Kuwabara looked at each other in confusion and then back to Botan. "What'dya mean, Botan?" asked Kuwabara.

Botan shook her head. "I can't really explain it. You'll have to get this one straight from Koenma."

Keiko then stood, a worried expression on her face. "They can't go now! School's only halfway over."

Botan smiled and nodded. "Oh, I know! I didn't come to get them at this moment." Yusuke and Kuwabara slumped in disappointment and Botan giggled. "Oh, cheer up you two! I came to tell you to meet me in the alley by the movie theater after school. I'll take you from there."

Yusuke groaned. "Can't we just go now?" he whined.

Keiko frowned at him and Botan shook her head. "The meeting time is this evening. See you then!" With that she took off, waving in her usual chipper manner.

Yusuke plopped back down and sighed. "Damn…and I was hoping to get out of school for the rest of the day. Man, I can't wait! It's about time we get to see some real action again! I used to complain about spirit detective work but I'm startin' to think it's better than all this monotony."

Kuwabara nodded. "Yeah…more action…more adventure!"

Keiko sighed. "And more danger," she added, her voice soft. Yusuke and Kuwabara sobered a bit and looked at her uncomfortably, not knowing exactly what to say. Keiko then smiled weakly. "But…I guess if you weren't here to do it, then it wouldn't get done and we'd all be in danger a lot more often."

Yusuke smiled and nodded. "Yeah, that's true. Hey, don't worry about us…we've survived some pretty crazy shit…we'll take on anything and beat it!"

Kuwabara grinned. "That's right! We're the good guys…we gotta win!"

Keiko nodded at last. "I know…I just worry, that's all."

She seemed a bit more reassured but not completely satisfied so Yusuke let her hug on Puu for a while. That always calmed her down and for the time being, it seemed to effectively make her feel better.

"Well, at least the little guy's good for something other than getting me laughed at," Yusuke mumbled to himself as he looked at his watch, starting to count down the minutes of the day.

The rest of the day seemed to crawl by. Yusuke and Kuwabara got more and more anxious as the end of the school day drew near. When the last bell finally rang, they met up and were just about to take off when a voice stopped them in their tracks. "Don't think you're going anywhere without me!"

The two turned around to see Keiko running up behind them with a stubborn look on her face. Yusuke frowned. "You can't come to a mission briefing! It's in Spirit World!"

Keiko looked more determined than ever. "I don't care! I'm coming! You're not leaving me out of the loop anymore!"

Yusuke crossed his arms and glared at her. "Not a chance in hell!" he said more assertively but Keiko didn't budge.

The two of them went back and forth for a while until Kuwabara looked at his watch. "Hey! We don't have any more time to discuss this! It's getting late!"

With that the argument was over and all three of them took off for the rendezvous point. Yusuke and Kuwabara tried to outrun Keiko but she was surprisingly swift and was able to keep up with them effectively enough for Botan to see her running up after them.

Botan frowned slightly. "Yusuke, you can't bring Keiko!"

Yusuke grumbled peevishly. "I didn't bring her! I didn't even invite her! She did that on her own."

Keiko finally ran up on them and stopped, panting heavily. "You jerks! Trying to...outrun me!"

Botan directed her attention to Keiko. "Keiko, I can't bring you too…Lord Koenma would kill me!"

Keiko was still trying to catch her breath but she looked resolute nonetheless. "I'm going, Botan. I'm in on this too. My life has been…in danger before…because of Yusuke's missions…I'm not going to just…sit at home and be a target…or sit around wondering…if you guys are still alive!" she said firmly, panting between the snatches of her sentences.

Botan sighed and gave up. She knew how headstrong Keiko was. "Oh…we don't have time to argue! Lord Koenma is waiting and he's not very patient! Get on everybody!" They stepped back into the alley and she materialized her oar and even made it stretch to be longer than usual to accommodate the extra passengers. With that, the four of them took off for Spirit World.

Upon arrival at Koenma's palace, Keiko was awestruck. She knew that being friends with Yusuke would expose her to things that she otherwise would never have been exposed to but this surpassed even her wildest dreams. She took in everything from the moment that it came into view to the moment that they stopped in front of the giant double doors that led into Koenma's office. Botan knocked and announced their presence and the doors opened.

There behind the desk sat what appeared to be a toddler feverishly pouring over books and papers. Keiko had only seen Koenma in his teenage form and she blinked in disbelief when she recognized the clothes. "Is that Koenma?" she asked in surprise.

Koenma heard her voice and his attention snapped up to the group now entering his office. He suddenly became very cross. "BOTAN! What's the meaning of bringing Keiko along?" He thought about transforming quickly, but what was the point? Keiko had already seen him like this.

Botan shifted nervously and cleared her throat. "Sir, I….I didn't….that is.…I…"

Keiko stepped forward. "I insisted, Sir." She then became somewhat sheepish. "You look…different…than the last time I saw you."

Koenma flopped back into his chair and sighed heavily. "Yes, yes…I know. This form…uh…conserves my great and powerful energy...yes…that's it."

Yusuke snorted out a snicker and then burst into laughter. "Yeah, right!" he scoffed.

Koenma shot him a look of loathing. Then he looked back at Keiko. "Never mind him! Just remember that no matter what my appearance is, I am very, very old and very, very wise."

Keiko nodded but Yusuke just laughed harder. "Well…HAHAHAHAHA…I'd believe old before I'd believe wise…HAHAHHAHAHAAA!"

Botan looked both shocked and angry. "Yusuke! Show some respect!"

It was Kuwabara, however, who smacked Yusuke on the back of the head just then. "Shut up, Urameshi! Did we come here for jollies or for a mission?"

Koemna offered Kuwabara an approving smile. "Ah, good man, Kuwabara. I knew I always liked you better."

Yusuke snorted wryly but he stopped laughing. "Ok, so what the hell are we here to do, anyway?" he asked indignantly.

"Well, perhaps if you'd stop farting around and listen, you'd get an explanation, dimwit!" came a raspy voice from the corner of the room behind them. Everyone turned to see three very familiar people step forward. Genkai had her gaze fixed on Yusuke as she had been the one to reprimand him.

Yusuke smiled half-sarcastically. "Hey, Grandma! Still as crotchety as ever, huh?" Genkai merely ignored Yusuke's irreverent greeting.

Kuwabara beamed happily. "Master Genkai! Red! Short stuff! It's been a little while!"

Hiei looked at Kuwabara with distaste. "Not nearly long enough," he said in his quiet but razor-edged tone.

Kurama merely smiled. "Hello. It's nice to see you all again."

"Sorry to interrupt your reunion," cut in Koenma, "but there's something very big happening and we don't have time for small talk. Actually…time itself is the problem."

Everyone now collected right in front of Koenma's desk and looked at him curiously. Koenma drew in a deep breath but leaned back, pausing dramatically and closing his eyes.

"SPILL IT, ALREADY!" Yusuke shouted impatiently after a few seconds of silence, pounding his fist on the desk.

Koenma gave him a very dirty look and straightened the papers that Yusuke had disturbed. "I'm trying to figure out how to explain this to you," he said, sounding harried. "It's very complicated."

After another moment, Koenma pushed an open book forward for everyone to look at. "Alright…as you all know, time is a very delicate thing," he said trying to sound official and pointing at a chart in the book. "Everything that is done results in consequences and if things were to be done differently in various instances of the past, future outcomes would fluctuate based on each unique action taken. Are you all with me so far?"

Looking across each face, he saw understanding in all but two. "Yusuke…Kuwabara…you have to pay attention and try to keep up! This is very important!"

Yusuke frowned. "Well, maybe if you tried not to talk like Albert frickin Einstein!"

Kurama raised a finger to catch Koenma's attention. "If I may?" he questioned. Koenma nodded and Kurama turned to Yusuke and Kuwabara. "Think of it this way, Yusuke," he said patiently. "Suppose you had the chance to go back to the day that you died…only this time you didn't jump in front of the car. Your future would turn out vastly different than it did originally."

Understanding lit Yusuke's eyes. "Oh, I get it!"

Kuwabara nodded. "Yeah, me too!"

Kurama merely smiled and returned his gaze to Koenma to indicate that he should continue.

Koenma sighed and nodded. "Ok…if the past is changed thereby changing the future, then the flow of time itself is altered and everyone remembers only the most recent outcome. In other words, no one would be aware that time was altered because what they would have originally remembered would technically never have happened and they would accept the new timeline as if it were always that way."

Again, Yusuke and Kuwabara looked utterly lost. Koenma's expression darkened and he groaned in frustration. "I can't explain this in any other way! Kurama…" he pleaded, his gaze shifting to Kurama as he waited for him to offer an explanation that Yusuke and Kuwabara could understand.

Kurama nodded patiently. "Let us use the circumstance of your death as an example again, Yusuke. If you had not jumped in front of the car and had never died, your future would not be as it is now, correct?"

Yusuke nodded somewhat impatiently. "Yeah, we already covered that, Kurama."

Kurama merely smiled and continued. "It follows, then, that none of this would have ever happened…thus, your memory would reflect a life without all of this. You could not remember it if it never happened."

Once again, the light of understanding clicked on inside Yusuke's and Kuwabara's eyes. "OH! I get it!" exclaimed Yusuke. "I couldn't remember dying and coming back to life and becoming spirit detective if none of that had happened!"

Kurama nodded. "Precisely, Yusuke. Your memories would instead reflect whatever life would have resulted from your choice not to jump in front of the car."

Yusuke frowned. "It would probably suck."

Koenma cleared his throat. "May I continue now?" Yusuke stuck out his tongue but Kurama nodded.

Koenma then took a deep breath. "Having said all of that, you must now realize that if time were fluctuating, none of you would realize it." He finally got nods from everyone. "Very good! I'm glad we're all finally on the same page. Alright…so here's the dilemma. Time is fluctuating. I know this because I exist out of time. It's one of my cool abilities," he said, suddenly looking self-important.

"The point," Hiei demanded succinctly.

Koenma deflated and frowned at Hiei. "The point, Hiei, is that this could be devastating to the present as we know it. So far, nothing major has changed, but if things are allowed to continue in this uncertain manner, the past could be drastically rewritten.

"May I ask what these changes might possibly entail?" Kurama requested in his soft, calm voice.

Koenma nodded. "I was actually just getting to that." He unrolled before them a long scroll with a timeline of the past 1000 years on it. "A new edition of this scroll is made every 1000 years. We make them to chronicle past events and to monitor any possible fluctuations in history due to instabilities in the time continuum."

He pointed to the timeline. "You see, these scrolls are outside of time as well. If history is altered, this timeline changes to reflect it." Sure enough, as he was speaking, a couple of events that had been documented shifted along the timeline slightly and another disappeared for a moment only to reappear again.

Everyone stared in surprise and Koenma sighed gravely. "I have been watching this scroll very carefully over the last few months. I have never seen time fluctuate so much as it is now and I've been trying to trace the source. I figured out that it's a time traveler who is causing this instability, because these changes started happening right after the first temporal disturbance we sensed…and only the presence of a foreign influence could cause a problem of this magnitude."

"A time traveler!" Kuwabara gasped as everyone exchanged looks of surprise.

Koenma nodded. "Yes…and it hasn't been easy tracking down the origins of the temporal gate, I'll tell you!"

Yusuke clenched his fists. "Who is this jackass? I'll take care of it!"

Koenma held up his hand. "Wait a minute, Yusuke. I'm not finished yet."

Yusuke rolled his eyes and slouched in frustration. "Well, hurry up!" he snapped.

Koenma ignored Yusuke's impatience and looked back down at the scroll as more things shifted. He shook his head. "Nothing earth-shattering so far but this is making me very nervous." He fingered a span of the timeline indicatively. He then looked back up at everyone.

"I don't know if any of you know this but several hundred years ago, the human world was riddled with demons. I'm talking about thousands upon thousands of them."

Kurama nodded. "Yes…as I recall, many demons migrated to the human world back before the barrier between the demon world and the human world was established. Demons were free to come and go as they pleased a little over 1000 years ago."

Koenma nodded. "Yes, and we established the barrier about 1000 years ago so that no more could invade the human world…at least not without great effort…but those that were already there were…shall we say…prolific. Some lines of demons had been there for centuries and some had just migrated right before we raised the barrier, but after a few generations there was a serious demon population problem even with the barrier in place."

"Not only that," continued Koenma, "but knowledge of Demon World was lost more and more with each new generation so that after a few hundred years, most of the demons of Human World had no knowledge that their ancestors came from an entirely different world. They completely adapted to life there and became a part of human history which made a mass removal even more difficult than it would have been already."

Koenma now leaned deeply into his chair, looking weary. "Frankly, we just didn't have the ability to deal with it. It took centuries just to develop the resources to get so many thousands back to Demon World. And then at that, they were so integrated into human life and history by that time that we had to remove them gradually or the resulting sudden change could have proved devastating."

"Luckily, as humans advanced in technology and science, they started to believe that demons and magic and such were just superstitions. After all, because of our efforts, the demon population was disappearing and it gave rise to a whole new way of human thinking. That made it so much easier to just remove the rest of the demons in bulk. Humans were ready to dismiss them from their evolving world…and we took care of it."

Koenma sighed and then continued. "Of course, we can never completely remove the influence of the supernatural in the human world. There are a few demons that somehow make it across the barrier from time to time without our admittance and then there are our affairs within the human world as well. That's why not all 'superstitions' have completely faded. There will always be facets of our three worlds that will coincide…it's what balances them."

Koenma finally paused and it was surprisingly Genkai who took the opportunity to speak. "Well, that brings us up to date in demon history within the human world but it still doesn't explain what we have to do."

Koenma nodded. "Yes, yes, I know…I'm getting to that."He looked down at the timeline and became very concerned at a sudden change but before he had a chance to get too worked up, it went back to the way it had been before. Koenma sighed deeply in relief and slumped in his chair. He then took a deep breath and continued.

"Like I said, we managed over time to effectively banish most of the demons from human world. But now that history is unstable, even that outcome could change. Based on what I've observed from this scroll, there is something that is giving the demons of about 500 years ago a massive advantage and allowing them to change history in ways that they shouldn't be able to. It started off small but it's reaching a dangerous level."

"How dangerous?" asked Kuwabara, though he had a feeling that he didn't want to know the answer.

Koenma looked a great deal more serious than everyone was accustomed to seeing him. "I would guess," he answered, "that if things aren't set right, the demons of the past will become too powerful to be removed from Human World. If that happens, it means they will also have the power to take it over. It could mean the complete destruction of humanity."

Hiei couldn't resist making the remark, "I don't see much of a loss there." For this he received several looks, but from Koenma he received an unwavering stare of severity.

"Don't make light of this, Hiei." Koenma chastized. "If the human world falls, the balance between the three worlds will crumble and everyone will suffer."

This caught Hiei's attention and though he had no intention of apologizing for his comment, he decided that this was now serious enough to merit his concern.

Suddenly, Yusuke piped up. "Ok, so then all we have to do is take down this time traveler, right?" He punched his fist and gnashed his teeth in anticipation of the fight.

Koenma sighed yet again. "No, Yusuke…it's not that easy. When the traveler first disturbed the flow of time, that set things in motion. Simply preventing this person from traveling anymore won't reverse the damage."

"Then what do you propose that we do, Sir?" asked Kurama calmly, as if he already knew the answer.

Koenma suddenly became resolute. "You need to go back in time 500 years and stop whatever is changing history, of course."

"WHAT?" blurted Yusuke before anyone else could react. "THAT'S your illustrious mission? Just go stop it! Well, hell, if that's ALL we have to do…"he bellowed sarcastically. "You blah blahed all that time just to tell us ultimately to go 'stop it'! What the hell kind of briefing is that?"

Kuwabara nodded. "Yeah, I gotta agree with Urameshi on this one! That's not much to go by!"

Koenma looked very frustrated. "I'd tell you more if I could but I've never dealt with anything like this before! I'm flying by the seat of my pants here, too, so give me a break, ok!"

Kurama was still calm as he asked, "Then how shall we proceed?"

Koenma heaved a giant sigh. "Well…I am going to accompany you all to the site of the temporal disturbance tomorrow…it's also most likely the dwelling of the time traveler."

Botan looked surprised. "You're going, Sir?"

Koenma nodded. "Yes, as serious as this is, I feel it my duty to confront this traveler along side my team. Besides, I have a feeling that this person has no idea how much damage their traveling has done. It might be best if I went along as a testament of just how serious this is."

Botan smirked. "Oh, so it has nothing to do with the fact that your father is returning tomorrow?"

Koenma paled and then scowled at her. "My father is coming back because of the urgency of this issue! I have to do everything I can so he'll see I'm taking this as seriously as it should be taken! Otherwise…." Koenma whimpered as he shuddered. His father was already angry that this situation had arisen in the first place and he knew he had better bend over backward to ensure as swift an end to it as possible.

His despair was interrupted by the sound of Keiko's voice. "So, then…this traveler lives right where the time portal is?"

Koenma snapped out of his trance of dread. "What? Oh…yes! Just last night, we finally tracked down the source of the temporal disturbance. It's coming from a small shrine called the Higurashi Shrine…home to the Higurashi family…it must be one of them who is using the portal."

"Why did it take so long to find it if this has been happening for months?" asked Yusuke with an annoying jeer in his voice.

Koenma cut his eyes at him. "Because, idiot…we could only track the disturbance when the gateway to the past was open…and it was always so brief that it was very hard to locate. It didn't happen very often either…sometimes weeks apart."

"Why didn't you summon us immediately when you found it?" asked Hiei. "If this is so important, why waste so much time?"

Koenma was getting very frustrated. "Because," he answered, "I needed each and every one of you for this mission but because of its nature, I couldn't just ask you to jump into it blindly on the fly. First, I needed time to do certain things myself. Second, I knew that you'd need this lengthy briefing. Third, I knew that you'd need the chance to make preparations."

"Preparations?" asked Kuwabara.

Koenma nodded. "Yes…I know this may not sound fair, but you'll be going back to the past and there's no guarantee how long you'll have to be there."

Kurama frowned for the first time. "In that case, one night hardly seems enough to prepare for a lengthy absence."

Koenma sighed, looking sympathetic. "I'm sorry but I can't give you more time than that. However, I have gone to great lengths to ensure that your affairs will be looked after. For those of you who this applies to, I have placed some of my people in proximity to your homes to watch over your families and I have assigned someone to collect your schoolwork for each of you," he said, looking at Kurama, Yusuke and Kuwabara. "If it is possible, I will have it sent to you so that you can keep up."

Yusuke scoffed. "I don't do my schoolwork anyway…what makes you think I'll do it while I'm in the middle of a mission?"

Koenma huffed at him. "Nevertheless, Yusuke, I'll be sending it if I can. Each of you do with it as you will."

Keiko cleared her throat, that expression of determination back on her face. "I want to go too."

Koenma blinked at her in surprise. "Keiko! It's far too dangerous! I'm sending the others in because they're my champions…fighters that have been designated for me to call on. But even though you're technically tied up in this, I'm not allowed to let civilians participate…especially defenseless ones. I'm sorry, Keiko, but under no circumstances will you be able to go."

Keiko was about to protest when Hiei turned to her. "Don't you understand, girl? You'd be a liability to all of us. You can't fight and you have no powers. We can't afford to go into this mission with someone who would require constant protection."

Keiko looked crestfallen and Kurama chastised Hiei. "Surely there were more delicate ways to put it, Hiei."

Keiko shook her head, however, a hard expression coming over her face. "No…he's right. I would be in the way with nothing to contribute. And I refuse to be a burden to anyone."

Hiei seemed satisfied with her answer and cast a glance at Kuwabara. "Now, if only the ape would acknowledge the same thing…"

Kuwabara towered over an unimpressed Hiei, grinding his teeth and shaking his fist in his face. "UP YOURS, TINY! I got plenty to contribute and I've already proved myself so you can just shut the hell up!"

Hiei looked bored with Kuwabara's ranting but he was definitely self-satisfied with his taunt.

Koenma cut in, however, before anything else could be said. "Alright! Alright! Knock it off!" He then turned to Keiko. "Thank you for being practical…not to mention saving me even more of my father's wrath."

Keiko nodded. Though she wasn't happy about staying behind, she truly didn't want to be a burden.

Koenma then leaned back in his chair. "Well, I guess the briefing's over. All of you go and do the best you can to make preparations for your absences. You three," he said, pointing at Kurama, Yusuke and Kuwabara, "don't worry about going to school tomorrow. I have already taken the liberty of writing elaborate excuse notes for each of you and am sending them with the same people who will be collecting your work."

Everyone nodded and then Koenma gave each person except Keiko a piece of paper. "Here's the address of the shrine. Meet me in front of it at exactly 1:00 P.M. That should give you enough time to make your provisions. See you tomorrow." He then went immediately back to pouring over the scroll and the books on his desk like he had been when they first came in.

Botan turned and ushered everyone out and they all went their separate directions. Botan took Yusuke, Keiko and Kuwabara back in the same way that she had brought them.

It wasn't until Botan had left and Kuwabara had gone off in the direction of his home that Keiko spoke again. "I guess…this is the last night I'll see you for a long time," she said, her voice thick with emotion.

Yusuke cleared his throat uncomfortably but then smiled at her. "Hey, don't worry. I'll be ok…and you'll be ok. At least you won't have me at school to get you in trouble or distract you from what you should be doing, right?"

He laughed a slightly forced laugh but Keiko's eyes began to mist over with tears even as she smiled sadly. "I'd rather have you there driving me crazy than off somewhere in danger and not knowing if you're ok." They reached Keiko's door and she turned to Yusuke, her eyes shimmering with sorrow.

Yusuke's expression softened. "Hey…don't worry," he said with a gentleness that he only expressed when they were alone. "I'll be back before you know it and everything will be fine."

Keiko looked into his eyes for a moment and then suddenly flung herself against him, clinging to him tightly, her tears spilling silently now that her face was hidden. Yusuke's eyes widened and he gulped uncomfortably at first but then after a moment, his arms closed around her in a slightly awkward embrace. "Keiko…" he uttered softly but made no attempt to talk her out of crying.

After a while, Keiko pulled back to look at him again. Because of the gravity of the situation and the proximity of their faces, there was a pull between them and the distance between their lips steadily decreased until they were but a breath away. Just before they touched, however, Puu poked his head out of Yusuke's backpack, which Yusuke had forgotten he'd been wearing this entire time.

Puu cooed softly but it was enough to break the moment and Yusuke pulled back and began to chuckle nervously, rubbing the back of his head. "Wow…it's pretty late!"

Keiko definitely looked disappointed but she smiled knowingly. Yusuke was still a big kid when it came to 'mushy stuff' as he called it. She still wasn't going to let him get away completely free, however, and she gave him a chaste kiss on the cheek.

Yusuke sobered instantly at this but then smiled cutely. "Heh heh…um…well…good night, then. I'll see you…later…"

Keiko gave him a serious look. "See that you do. You better come back, Yusuke."

Yusuke nodded. "Count on it."

Keiko then smiled and turned to go but she hadn't even taken a step before Yusuke reached up under the skirt of her uniform and squeezed her ass like he always did. She blushed and turned around and smacked him hard.

Yusuke grinned at her even though her handprint adorned his cheek. "Had to get one more in…I won't be able to do it again for a while."

Keiko couldn't resist the smile that tugged at the corners of her mouth. "You big dork. Good night. And take care."

With that, she finally went inside. "Good night…Keiko," he whispered after she'd already shut the door. He stood there for a moment even after the front light had been turned off and then walked home by himself, his mind racing with everything he'd been told and everything he had yet to face.