The jar containing the elixir of immortality was brought to the emperor in his grand palace. There he lay weeping, eager for any news of Kaguyahime. Upon receiving her gift and final letter, he knew that she had gone, and his heart broke anew for the knowledge that he would be without her light forever more. Thus he summoned to his side one of his mighty generals, a man named Iwakasa and bade him carry the jar containing the elixir of immortality to the land of Suruga. There a great mountain, closer to the sky than any other, towered over the earth. The emperors will was that Iwakasa should bring the jar to the peak of this mountain, as close to the moon as any mortal could reach, and there burn it, that the smoke of the elixir might reach to the heavens and carry the message of the emperor's sadness to Princess Moonlight.

Iwakasa gathered to him many of his most loyal samurai, and together they ascended the mountain. Seeing their numbers marching to the peak, the people of that land gave the mountain the name 富士山, using the kanji meaning 'mountain abounding with warriors.' When the elixir was burned it created a inexhaustible flame that would never go out, and the smoke still rises to this day. For this reason the Emperor declared that 富士山 should be read as 'Fujisan', taken from fushi - meaning 'immortality.'

"So... is that the end of your story?" Eirin asked.

"Yes. Thank you for your attention." Renko nodded her head.

"I see. What is it that you hope to achieve by telling me this tale, I wonder?"

Her eyes were narrowed. She hadn't denied a word of it, and the story painted her as someone willing to kill to protect her deceptions. I couldn't help but cringe away. Renko, however, was as unconcerned as usual. "If anything, I'm hoping you'll refute it. What I was expecting you might do is tell me a different story, some irrefutable truth that would shatter my theory to its foundations and disprove my hypothesis. As a fellow scientist I'm sure you understand the value of an experiment that disproves a theorem."

Eirin reacted with surprise. "You're looking for me to reject your ideas?"

"I don't claim to have any ownership of the one and only absolute truth. The existence of an objective, absolute answer is something that has largely been rejected by modern science. I'm hoping that if there's information I'm missing or I've made a miscalculation, you'll point it out to me, and provide evidence to the contrary."

"Then I suppose there nothing more for me to say," Eirin admitted with a sigh. "Unless of course you're planning on relaying this story to Kaguya unless I deny it?"

"I see no need to fill the princess' head with such fairy tales, seeing as she's already the subject of one. Besides, she's known you for far longer and trusts you far more than she does me. If I were to tell her my story, you'd just shoot it down immediately with some plausible-sounding denial. You could keep that up as long as you like. Even if you're not truly immortal, you and the princess will live far, far longer than I will, and even if I were able to convince her, you'd undo my influence in time. This story is simply something I've made up for my own amusement, to see if you'd have a good alternative to tell me instead."

"Well in that case, I see no need to take further action. Let's leave it at that."

"Well, thank you very much then. I'm grateful to have had such a receptive audience." Renko stood and doffed her hat, then bowed again before offering a hand to help me to my feet. I rose and bowed to Eirin as well, following as Renko turned to leave. As she reached for the door though, Eirin called out to stop her.

"Your name. It was Renko Usami, was it not?"

"Yes, that's me, the famous detective."

"I'm a bit surprised, do you not wish to become immortal? I expected you to ask me to make another dose of the elixir as a sort of blackmail," she said with amusement.

Renko turned slowly at these words, easing her hat back onto her head as she did so.

"That... is a very tempting offer, especially considering its not actually absolute immortality you're offering me. I'm going to refrain for now though."

My eyes widened in surprise. This whole time I had been thinking back to that conversation I had had with Renko so long ago on the terrace of the campus café. Back then, Renko's answer to the question of if she'd drink an elixir of immortality if she had the chance had been 'of course!'

"Really, Renko? I'm surprised." I said.

"Really Merry? I'm surprised you're surprised. Wasn't it you who said you weren't ready to take care of old lady Renko forever and ever?" She fell to one knee, posing dramatically like an actor in a play, her head tilted back with one hand laid on her forehead. "If I must spend eternity alone without the light of Merry in my life, then I must chose oblivion as the lesser of two evils. Unless..."

Suddenly she rose up and bounded forward in one motion. Reaching out, she grabbed both of my shoulders, holding her face close to mine. Looking into my eyes with an excited smile she asked "Merry, do you want to be immortal? If I'm going to be around for that long, I'd want to have you by my side." I turned away from the intense eye contact, looking down and willing myself to stop blushing as her question echoed in my mind.

I had never given it deep thought, as the question had always been an impossibility before. Having read story after story describing the misery of it, however, and even seeing how Mokou had dealt with it, my gut response would be to instantly say 'no.'

And so I did. "I don't think I'm crazy enough to make a snap decision on eternity, Renko. I don't know if I ever will be." I shook my head.

Renko released me and turned back to Eirin. "Well, there you have it," she said.

Eirin actually smiled for once, not in the calm, professional way she had for the sake of mere politeness before, but genuinely, with real warmth. "Well, alright then. I'm certainly still going to be around if you ever change your mind. If you should decide to then come back and see me. As long as the princess approves, I think you'd be welcome to join us here in Eientei, where all of us could be together forever."

Renko flashed her a grin and tipped her hat. "I'll be sure to keep that in mind."

With that, the doctor turned her back on us and retrieved her writing desk. Renko and I made our way out of the room and back down the hallway to the entrance. Although the path was completely straight this time, my mind was turning in endless circles the whole way.

-.-.-.-.-

And so, that was the story of our involvement with the Eternal Night Incident. If you were to sum up all of my partner's delusions this time around, I suppose you'd call it a tragic story of two lives and deaths hopelessly entangled.

To those who live on the moon, both life and death are a foulness to be rejected and avoided at all costs. Living in ascetic austerity and avoiding attachment, the people of that place did everything in their power to live forever. To reject that life was to embrace death, the one true taboo in that society, something so unthinkable that it would never be allowed to anyone who lived there. In search of a way to escape that deathless, lifeless existence, Eirin and Kaguya had come to Earth, earning an eventual slow demise through the abrasion of their souls with the coin of a falsely eternal life.

That was the existence Eirin had chosen for them, a long, peaceful repose of isolation and soul-searching.

Could it be that such paradoxical thinking might actually bring them closer to the truths of existence than any other? Or was all of this simply a fantasy story created by my partner's overactive imagination?

Only Eirin knew the whole truth, and she had neither confirmed nor denied anything in the end.

-.-.-.-.-

On our way out of the mansion grounds we were caught by Tewi and her Inaba, who drew us aside, to attend a moon-viewing party with Kaguya, who had returned from her visit to the shrine.

"Oh, it's the two humans from the other day," was how Kaguya greeted us. "Did you two get all fixed up by Eirin?"

"What do you mean by 'fixed up'? And what were you doing at the shrine, princess?" Renko asked.

"Oh I was just inviting the people there for a bit of fun and games."

"A game? With the shrine maiden? What kind?"

Kaguya giggled behind her sleeve. "Oh, you'll see soon enough. Until then, why not sit and watch the moon with me? It's very pretty tonight."

And so we all sat down on the porch outside of Eientei, eating the mounded dumplings that Reisen brought out and looking up at the moon as Tewi and the Inaba frolicked in the courtyard.

"Renko, didn't Eirin say you should avoid looking at the moon too much from now on?" I chided.

"Well if I go blind again then I'll get to have Merry take care of me again. Almost makes it seem worth it. -These dumplings are delicious by the way."

"Maybe I don't want to take care of old lady Renko anymore."

"Oh no, that sounds pretty serious. Who will provide for me in my old age? Maybe I better go ask Eirin to make me immortal just so I don't have to worry about it."

"That'll be decades from now, Renko, long after we're done with university, assuming we ever get back to it. Do I still have to stick around when I'm a wrinkly, old granny?"

"Absolutely, Merry. Loneliness among the elderly is a big concern. I need you to stick right by my side."

"Well it's not like there's anywhere else for me to go now that we're here anyway. Or has this all been a plot to keep me close at hand from the moment we first went into your aunt's room."

Renko feigned a guilty expression and turned to Tewi. "Uh oh, she's onto me!"

Tewi laughed. Reisen was sitting behind them, looking unhappy as usual, watching the moon with a slightly nervous expression as her ears twitched. Tewi noticed and gave Reisen a friendly elbow in the ribs. "Come on Reisen, why the long face? You should be enjoying the moon viewing with us."

"I'm glad it's easy for you to enjoy. I had to prepare all these dumplings myself while you and the Inaba disappeared," she grumbled.

Kaguya turned to smile at Reisen. "You really do seem down. Are you disappointed you didn't get a chance to return to the moon after all?"

"What? Uh, no princess, not at all."

"That's good to hear," Eirin said as she emerged from inside the mansion. "I'm afraid I can never let you leave Udonge, you're simply indispensable for my research."

Reisen's mood seemed to brighten at that as her red eyes widened in surprise. "Thank you, master!"

"Well it's true. The princess isn't about to do the laundry, cleaning or the cooking and now that the wards of eternity around the mansion have been released there's going to be a lot more chores to take care of. My research is far too important to disrupt, of course."

Reisen's ears drooped. "Oh, so that's what you meant."

"Well, whose fault is it that the intruders got in and broke all the seals in the first place? It's only natural," Kaguya added with a smile.

"That's right," Eirin said with a nod. "We'll expect a lot of hard work from you going forward. Oh, unless you'd rather I use your body for experimentation. It's been quite a while since I had a live lab rabbit to work with."

Reisen's ears fell limper still, now lying flat against her head. "Laundry sounds good, thanks. I'll work."

Eirin smiled as Reisen's shoulders slumped and Kaguya giggled behind her sleeve. After a moment Kaguya let out a sigh and spoke again. "My, I wonder what's taking them so long. I would have expected the show to start by now."

All at once the Inaba in the garden began to make a fuss, hopping around agitatedly. We turned to look at them and our eyes caught the flash and sparkle of colored lights on the far side of the garden wall, as if someone further on in the forest were playing danmaku.

"Oh goody, it's begun!" Kaguya said as she clapped her hands together. In the distance a spiral of red flame lifted into the air before exploding outward into a shape like a pair of fiery wings.

"Is that... miss Mokou?" I asked as I watched the flames flicker in the sky.

"Now this is a proper spectacle!" Kaguya announced gleefully. "Let's watch Mokotan get exterminated while we enjoy these nice dumplings."

I looked over at my partner with concern. She looked worried as well, but with them already high in the sky and engaged in a fury of bullet barrages, there was nothing we could do. Kaguya's joke may not have been to our tastes, but having either of us get injured by a stray bullet wouldn't make for much a punchline either.

Still, with Renko you never could tell. "Renko, don't go running off, you'll just get hurt."

She sighed. "Well the killer in this case is already sitting right beside me, so I've got nowhere to go. I don't like it, but since it's Mokou, I'm sure she'll be fine."

An explosion boomed overhead, followed by a flare of light in the shape of a phoenix then a frantic flurry of bullets twisting off into the night sky in every direction at once. "The Earth can be very beautiful sometimes, even amidst all the death." Kaguya mused.

Eirin watched the battle, as flickers of red light highlighted her cheekbones and making the red half of her dress seem to glow. "I agree," she said placidly.

I looked over to see Kaguya leaning in and whispering something to Eirin behind her drooping sleeve as they both smiled. As twisted as the morals of either of them might be, they had their eternity together on this Earth, just as they had always wanted. Watching the multicolored light of the danmaku washing over their smiling features, it was hard to think of all of their sins and machinations from so long ago and think of them both as entirely evil. At the very least, it would be hard to say anything just now.

-.-.-.-.-

After the moon-viewing and the danmaku viewing, we politely excused ourselves and left Eientei. Without Mokou to guide us, the moonlit forest was intimidating, but the recent battle had cut and burned enough swathes of the foliage that we were at least able to find our way to Mokou. She was laying flat on her back in the middle of a scorched patch of leaves and flattened bamboo. Uninjured, but spread out on the ground staring up at the moon. Her clothes were ripped in places but otherwise she seemed completely unbothered as Renko helped her to her feet.

"So that's Reimu." she said with something between appreciation and a grumble of disapproval. "I'd heard stories, but I see why everyone's scared of her now."

"Oh so that was Reimu. And Marisa too, from the danmaku we saw. Are you OK, Mokou?" I asked.

"Yeah, that was them alright. Kaguya tricked 'em into coming here, saying it was a test of courage. I'm fine though, it's not like I could die, so I don't really mind."

It seems it was much as we had suspected from our view at Eientei.

"That's rather magnanimous of you. I hope they didn't hurt you too bad, Mokou," Renko said.

"Are you kidding? They must have killed me a dozen times. Those girls are pretty tough. Honestly, Keine was worse though. Trying to calm her down after her work gets interrupted is nearly impossible." She gestured to her side where Keine was softly snoring on a bed of mounded bamboo leaves.

"I guess there's a lot of strong and interesting humans out there nowadays," Mokou muttered, then looked up at Renko. "You guys are pretty crazy if you're hanging around with people like that on a regular basis. Has everyone become like this in the last 1300 years?"

"Well, not everyone, but that's progress I guess," Renko grinned.

"Huh, I don't know if teenagers capable of that kind of violence could be called progress. Maybe it'd make for a fun vacation if everyone were like me, but those two girls were just humans. They could dish it out, but if I had really fought back, it would have killed them."

"This world is full of humans who can die. But a human that can't isn't so different either. There are already Youkai who can barely die, ghosts who are already dead and gods who don't even need bodies. Gensokyo has all of them. Would it really be so bad if you went out and made a few friends among them who may or may not die?"

"Sheesh, when you put it that way I sound kind of pathetic."

"Ah, sorry, I went too far then. I'm just happy you're OK, Mokou." Renko bowed her head apologetically while sticking out her tongue.

Mokou sighed and stretched, reaching up above her head. Just as she brought her arms down, a hint of crimson at the very edge of the horizon signaled the first light of dawn.

"You know," she said, "for the past 1300 years I've thought about what I'd do if I could find a way to die. Maybe I'd kill Kaguya first, or maybe I'd kill myself and leave her to suffer alone. Either way though, I thought I'd want to die as soon as I could. Right now though..." She looked down at Keine again, then back to Renko. "Maybe being alive a bit longer isn't so bad."

-.-.-.-.-

By now, the Eternal Night Incident had fully ended. Perhaps, in the spirit of sticking to the subject matter of our detective agency's mysteries, I should end my retelling here as well. But for sake of completion I hope you allow me to include a few more words regarding our own story.

A few days after the our last visit to Eientei, in the evening, just before we were about to close up shop for the night we had an unusual visitor. When I opened the door to a knock, there she was, the red and white miko herself, a rare sight within the village.

"Reimu?"

"Hi. Sorry to bother you so late. What is this place, some kind of business?"

Renko, who was sitting at her desk looking through a copy of the Bunbunmaru Shinbun she had picked up in town piped up. "The business just closed for the evening, so right now this is just the forward outpost and secret hideout of the Hifuu Club, where we work to reveal the secrets of the world.

Reimu blinked and stepped into our room. "I never understand the way you Outsiders think," she sighed.

Helping herself to a cushion, Reimu took a seat across from Renko. I grabbed a cushion and had a seat beside her as well.

"So, you guys have been here for over a year now, right?" she began. We had first wandered into this world at the height of summer the year before, and it was early autumn now. We nodded in agreement. "Well it's a little late for this then, I suppose, but do you two have any intention of returning to your own world?"

We looked at eachother without thinking. "Can we go back?" I asked. "To the Kyoto of the Scientific Century? 80 years from now?"

Even after everything we had seen it was still difficult to accept. No explanation of how we had travelled back in time had ever emerged or even suggested itself to us in the time that we had been here. And yet, our having done so remained an indelible fact. It spoke volumes to how accustomed I had become to life in this world though that upon hearing the question from Reimu, my response had not immediately been "Yes! Right away!"

Renko, meanwhile was more hesitant. "If the option to return home presents itself, I'd certainly want to keep it open, but right at the moment I can't say that I have a strong desire to find a way back no matter what."

Reimu let out a sigh at that. "That's what I figured. The Crimson Mist Incident, the Spring Snow Incident and now the Eternal Night Incident. Actually, come to think of it you were at the banquets with Suika too. That's four times you've shown up in the middle of an Incident, and ended up getting close to the masterminds behind the events before I did. Even with Suika, you found her first, didn't you?"

"Yes, that's right."

"Four times. I was willing to believe it was a coincidence the second time, but by this point, no way. Who exactly are you two and what do you have to do with all of these problems that keep occurring? Especially you, Merry." Reimu pointed her finger and glared at me, though at this point I suppose I should be grateful that it was just her finger she was pointing and not her gohei. "You look just like Yukari, and you're at the center of every Incident, but you seem to just be a regular human. What's your deal? Are you Yukari projecting a human illusion? Or are you working with her or what?"

I shook my head back and forth in a panic, grimacing. "It's a complete misunderstanding! I don't have anything to do with Yukari and I don't want to. The only reason I keep being involved in Incidents is to due to her tendency to shove her nose into every foreboding mystery she can find." I jerked a thumb at Renko.

Reimu glared at me a minute longer, then let out a heavy sigh. "As unlikely as it seems, I believe you. You don't smell like Yukari and you seem to be a completely harmless human."

"That's me, totally harmless." I tried my best at an endearing smile.

"But youkai or not, you're still suspicious. You're not only from the Outside world but from the future as well. As far as I'm aware Yukari's never spirited away someone from another time before. That's why I asked her about you. Including if she could send you back to your own time."

Renko leaned forward over the desk. "Well, what'd she say?"

"She played dumb and said she didn't know anything about it and wasn't the one who brought you to this world. Who knows how much we can trust anything she says though."

I thought back to the first time I had seen Yukari, at the end of the Spring Snow Incident. How she had produced the amber we had found in Sumireko's room from nowhere and had me deliver it. What connection could there be between the youkai sage and Renko's great aunt? What role had she played in bringing us here?

"When I asked her about sending you home she said 'Even I have difficulty manipulating the boundaries of time. Moving someone through 80 years of it would be very difficult'" Reimu mimicked the youkai sage as she talked, speaking with her eyes half lidded and an imaginary fan over her mouth as she took on an airy, disinterested voice.

"So that means..." I couldn't bring myself to say it.

"...That there's no way for us to return." Renko finished my thought. "Well, maybe that's the case anyway. Or maybe Yukari is lying and doesn't want us to go back yet for some reason, though that's just a hunch. Do you have any idea what she might want from us?"

"Ugh, don't ask me to imagine what she's thinking. Whether she's lying or not though, it looks like you're going to have to get used to living in the human village for the time being." Reimu stood up from her cushion and glared down at Renko. "In which case, I don't want you getting any more strange ideas."

Renko blinked and smiled sweetly. "Whatever do you mean?"

"Humans are humans." Reimu said flatly. "Don't get an idea into your head to try and be anything else." With that she turned and headed for the door. "I'll be watching you," she said as she walked into the night.

Renko went through the door a moment later, waving her arm over her head at Reimu's departing form before coming back inside and shutting it.

"You know, my life has gotten pretty messed up because of you, Renko," I said as she came back in. "Before I met you I managed to go more than two decades without once being attacked with a sword or being threatened by a miko or almost being flattened by an oni or being at risk of having my brain removed by a mad scientist."

"Well that's hardly my fault. If anyone, you should blame my great aunt. For now though, we should just enjoy the ride. The youkai sage may well change her mind once she's done with us. We just have to be patient."

Renko flopped over on the tatami and stretched out. If somehow we were to go back to our own time tomorrow I probably wouldn't be able to help missing Gensokyo at least a little. A year was all it had taken for a love of this world to seep into us. "If we were to wake up in the scientific century tomorrow I wonder if we'd even remember how things worked? We'd probably be like a pair of cavemen staring in horror at everyday conveniences for at least a little bit," Renko said as she stared at the ceiling. "Besides, if we went home now we'd be leaving so many mysteries behind! There's still a lot of this world I want to see."

"We've been pretty much all over at one point or another by now. What's left that you want to explore?"

"There's whole worlds we haven't explored yet! Like Makai or the Underworld. What about the heavens? The dragon god has to live somewhere, right? We haven't even really gone that far up Youkai mountain either. I'd like to see the tengu city, or wherever the kappa have their workshop. Oh, and of course there's the moon! We never got to go in our own time, but maybe we can have a moon tour here someday, Merry!"

"After everything we went through with Eirin you still want to go to the moon?"

"Hey Merry. Think about this. Eirin and Kaguya had been hidden on Earth in the place that would eventually become Gensokyo for a long time, but Reisen only came here a few decades ago. The Great Hakurei Barrier would have already been up by then. What do you think that means?"

I blinked in surprise and thought about it for a moment. "That means..."

"That the moon here isn't the same one in the sky of our world. It's a different moon, one with a whole Lunar Capital on it somewhere. It's connected to Gensokyo, just like the Netherworld. The moon we see in the sky here is the mysterious, magical moon that was forgotten by humanity in the 1960s, when it became just a barren hunk of rock in popular perception."

Saying this, Renko sat up stiffly from the floor, her eyes sparkling with wonder. "I wish we could sneak back in to Eientei to see if they had a way to go back to the moon. I need to find an excuse to go see Reisen again too. There's a lot of things I'd like to test with her eyes. She could be a whole new field of physics unto herself!"

"Hold it right there." I said, raising my hand, palm up. "Before you get lost down a mental rabbit hole we need to deal with a more immediate and pressing problem."

"And what's that?"

"Dinner."

As soon as I spoke the word Renko's stomach began to rumble. She blushed and covered it with her hands. "Betrayed by my own stomach! Bah, you can't reason when you're hungry anyway. Let's go Merry, there's a new place we can try."

"A new place? What's wrong with the old one?"

"I was reading about this in the paper. There's a night sparrow youkai who's been allowed to open a food stall that serves humans and youkai both just outside of town. Their specialty is grilled lamprey, how's that sound?"

"Lamprey? Those are the creepy fish with the horrible mouths, right?"

"Sure. I hear eating them is supposed to be real good for your eyes."

I sighed as we walked out the door. "Alright, why not. What's one more life-threatening adventure?"

-.-.-.-.-

Thus, we closed the door of our detective agency much as I will close this story, with the two of us walking hand in hand, out into Gensokyo's mysterious night as the moon hung in the sky above, with all of its bright magic shining silently down as always. The light of that moon no doubt fell upon many others that night, each of them with their own stories, desires, needs, wants and struggles. Each of them an entire world unto themselves, filled with countless fascinating mysteries.

If one of those moon-mad mysteries inhabiting your own life should ever consume your nights, keeping you up in search of an answer, then feel free to stop on by the the storehouse behind the temple school some time. My partner and I will be eager to listen.

This has been the fourth report of the Hifuu Detective Agency, two girls together, illuminating a starlit path through the mysteries of the night.

[End of Book 4: Imperishable Night]

-.-.-.-.-

Author's Afterword:

Thank you for reading through all of that. I am the author, Shinobu Asakihara.

The solution to this mystery, concerning Eirin, Kaguya and the Hourai Elixir is actually something I've included in some of my previous works. It shows up in both the full length story "Umiyonge!" and the short story "*****" published in other collections.

I would not want to just use the same ending over and over however, so this time I added a pair of new twists, I think they made things better.

The setting and description of my moon related stories changes from time to time as my conception of the nature of lunar society changes, much like the face of the moon itself. I hope you liked this particular fantasy, but if not, don't worry. Even Renko would tell you that the moon is full of mystery and shows a new face every 28 days.

Please continue to follow along on Renko's next grand delusion, coming soon.