A/N:

Yes, ladies and gentlemen, your eyes are not deceiving you. I am writing another story.

God, what is wrong with me…?

Anyway, since I'm going off to college next week, I figured: 'Meh. Why the hell not?'

So, I don't want to make this Author's Note very long (you guys are probably ignoring it anyway), all you need to know is that this is kinda-sorta-very-loosely a crossover, but they don't have the category for the other one (I won't tell you what it is) and the fine details of the other world (still not telling…) will be explained later. The other story (…okay, it's a manga) is mostly about this guy whose parents – and years later, his brother – got killed by this mad man who is trying to rule the world by using the protagonist's body which is very compatible with the corrupting power he owns and wouldn't disintegrate like his other vessels. The story is (awesome!) mostly centered around Celtic mythology.

This fic is Nico-centric. Since it's a time-travel fic (I love those!) some of it is just a retelling of what we already know with the scenes involving Nico tweaked here and there. The parts that appear in the PJO and HoO verse will be in the other characters' – mostly Percy's – POV, but the ones that don't are all Nico's POV. Most of the fic's setting is in London (like the manga) and Nico's life there. There will be OCs (some of them are just borrowed characters from the manga). Lots of 'em.

Now, for the pairings. Fair warning, I've been a Percico shipper since before even The Last Olympian came out and I was very happy to find out that it was kinda-canon in House of Hades. But I don't really have any problems with the Solangelo ending either, so this fic could go either way, but I'm leaning more towards Percico. And don't worry guys I already have people in mind for Will and Annabeth to end up with in the end. Trust me, you won't see it coming…

Now, most of the time Nico will be OOC which is expected of time-travelling characters. He'll be more mature, a little less unsure of the future of the others, but unlike most time-travelling characters, I made him very, very hesitant to change anything in the past. I got the idea from a discussion I had with my friend and he said that if he returned to the past, he would try to change as little as possible because he feels more reassured with a fixed future he already knew than an altered future he knows nothing about… and, to me, Nico's always seemed like one of the most cautious characters in the PJOverse (when it involves anyone's safety but his own). He'll do anything he can to keep his friends and family safe and happy and changing the timeline seems like it would put that at risk.

…Well, so much for keeping the A/N short.

Either way, now that you've read all this, the usual rules apply: DON'T LIKE, DON'T READ. If you have a problem with the setting of my fic, you can criticize but don't flame.

For the rest of you, enjoy ~

Warnings: Slash, OOC, AU, crossover-ish, spoilers, some gore, typos, un-beta'd, late updates, weird Brittish English & American English combo.

Summary: They won the war and diverted the apocalypse only to be wiped out by another unexpected apocalypse. There was no warning, no prophecy, no omens, they were all taken completely by surprise. All except Nico, who couldn't feel surprised over anything anymore, because he was one of the first to die.

Well, he was dead… until the personification of Time brought him back to life then, sent him to the past with orders to, "Find the one responsible for the end of the world and stop him." Easier said than done, Chronos.

Disclaimer: No. Just, no.

xXXx

Prologue – his revival

Nico groggily opened his eyes and regretted the action almost immediately. It was so bright!

"Urgh!" he groaned as his eyes slowly – painfully – adjusted to the light. He blinked a few times before he remembered…

Dead people didn't need to blink.

He was dead. Or, well, he was supposed to be.

"This is him?" Nico heard someone say in distaste. Then, he felt something hard jab his ribs. "He is a lot… smaller than I expected."

"Is he still alive?" a voice softer than the first asked. This time, he felt something thin poke his back gently.

"I do not know," the first person spoke again. "It's so difficult to tell with mortals..." Nico felt something – that he was starting to suspect to be a foot – jab his ribs again. "He looks dead, but-"

"Chronos, stop kicking him," the second voice cut in sternly.

Wait, Kronos!

Nico groaned again – louder, this time, and with a heavier dose of exasperation. He thought being dead meant that he wouldn't have to deal with anymore life-related drama.

He felt someone – (Kronos!) – kick him again.

Ow!

"Chronos…"

"I was just making sure that he was still alive!"

Yes, Nico's eyes were open and he was really fighting the urge to close them again and sleep. He sat up, slowly and reluctantly. He felt like he'd shadow travelled around the world a hundred times over while starving and transporting a dozen obese elephants with him.

Okay… so that may have been an exaggeration. He only had to travel half-way across the globe and he wasn't exactly starving, just underfed. And instead of twelve fat elephants, he only had to transport himself, a half-goat man, a Reyna, oh and an Athena Parthenos.

So, really no one could blame him for passing out afterwards.

…No, that's not right. He didn't just pass out. Shadow travelling had always been one of his most taxing abilities. The fact that he had been able to deliver Reyna, Coach Hedge and the entire Athena Parthenos back to camp in once piece was an impressive feat in of itself. To do it while he was still recovering from his trip to Tartarus was nothing short of a gods' damned miracle. He had to use every drop of energy he had left in his sickly body, so naturally at the end of it he would have…

"…died," he spoke for the first time in what felt like forever, judging by how dry his throat felt. "I died," strangely, this revelation didn't surprise him one bit, "after… I shadow travelled and… and, then…"

"And then the Seven Half-bloods of the prophecy defeated Gaea and won the war," one of the unknown beings said in a monotone drawl, like the achievement was no big deal. "But, while everyone was busy with Gaea, another powerful baddy was getting busy and killed everyone with an army of monsters while the gods and heroes were occupied with the victory party."

"What?" he asked incredulously. He would have shrieked or yelled in disbelief (because seriously WHAT), but his throat was too sore for that. "That can't b-" he shook his head. "But, Percy and- and Hazel and the others…! The Prophecy of Seven…!"Then, they went through all of that – fought two wars and averted apocalypse after apocalypse – for nothing! They defeated Gaea and her army of Giants only to be killed by another army?!

"Mentioned nothing of the other Big Bad," the same person finished. "He caught everyone – Greek and Roman – by surprise."

Nico finally looked up and studied his surroundings. He was lying on what appeared to be… a slab of broken cement. Around him, pieces of buildings and cars and trees and everything else you could think of lay scattered in a chaotic mess as far as the eye could see. Strangely, there was no sound. Everything was quiet.

Then, he took in the others.

One was a small boy with curly brown hair and deep dark eyes. He was very young and he was standing over Nico with his head tilted and his eyes narrowed curiously. He was wearing open toed sandals and a white toga – it was Ancient Greek garb, something Nico had seen many of the gods wear before.

The other person was a woman – more like a teen really. She was different from the other in many ways. For one thing, she seemed to be translucent, like much like the spiris Nico spent a lot of his time with. She was wearing – strangely enough – a dark green European dress. It was a very old dress too, like something you'd see people wearing at a Renaissance Fair or during the actual Renaissance. Her hair was long and blonde, left untied to cascade down her back in golden curls.

Huh, Nico's never seen any god – Greek or Roman – wear an outfit like that before.

With so many questions swimming through his head, he felt like he should ask the first one to properly form in his mind. "Why is this place so quiet?" It was a testament to how greatly confused he was if that was the first question he could properly ask.

"Do you have any idea where we are?" the boy – who had kicked Nico earlier and who he was now suspecting to be a younger version of his paternal grandfather, if the name he'd been called was anything to go by – asked in return, completely ignoring Nico's earlier question.

Somehow, Nico felt like he really didn't want to know the answer to that question, but he answered the boy-titan-god-whatever anyway. "No," he said as he continued to observe his surroundings. He didn't recognize anything here – which was completely understandable since the only time he'd seen so many destroyed buildings in one place was during the war against Kronos and the Titans.

"This is New York," the ghost-like lady answered. "Three years after that… that being launched his first attack."

Nico was sure that his heart stopped beating for a second. The blood in his veins grew cold. He had been right. He didn't want to know the answer. He felt like he was going to throw up.

It can't be…!

If this was New York, then what did the rest of America look like?

What happened to Mount Olympus and the gods now that the Empire State Building was gone?

What happened to Camp Half-Blood, to Camp Jupiter and all of the campers?

What about Hazel and Jason and Annabeth? What happened to them?

What happened to Percy?

"Where is everyone…?" he asked with heavy dread. He didn't want to know the answer to that question either. The fact that he could not a sense a single Life Aura anywhere was enough to answer that question.

This was the result of one god, giant… being… whatever! One being (because they had only mentioned one 'bad guy') had been enough to do this much in just three years! Why didn't anyone do something?! Why did no one stop him?!

No, wait… Nico knew why. They said that this happened immediately after the Giant War. The demigods must have been too tired from the battle. And they did say that the gods had been too busy (probably too relieved) to see the attack coming-

"Why didn't anyone see it coming?" he asked out loud.

"The first attacked happened in London," the boy answered. "London is," the boy took a moment to glance at their surrounding, "well, was the epicenter of many pantheons at one point in time or another. The Greek and Roman gods weren't the only ones to have influence and power there. The Olympians must have sensed that something was amiss in London, however with the imminent war against the giants they were facing, they must not have given it much thought."

Okay, setting aside the shock at learning that there was such a thing as other pantheons out there (Nico wasn't too surprised, he'd used up most of it when he learned of the existence of the Romans), Nico asked with disbelief, "If they knew that something was wrong, couldn't they have just sent someone to check things out in London? You know, to see if it was anything bad, just in case?" Although he knew whining about what could have been done was pointless now that it had happened, Nico couldn't help but wonder.

"They must have assumed that another pantheon was the cause of it." Seeing that Nico was about to ask some other ridiculous (to Chronos) question, the boy quickly explained. "No divine being is allowed to ever meddle in the affairs of other pantheons. It is every pantheons most absolute law. The consequences would be dire. In the past, many gods have faded or been consumed by their more powerful counterparts because of this. Their followers would wage war with one another to prove that their own gods were better than any of the others. Take the disaster that happened between the Greek and Roman demigods for example."

That might have happened some thousands of years ago, Nico argued in his head, but the world's changed. This time, there was no disaster. There had been no war between the Greek and Roman demigods. Sure, it was a close call, but Nico and Reyna had arrived and stopped them in time. And if they did win the war, then that must have meant that Reyna had somehow been able to convince all of them to work together.

"Well, that was the case," the boy amended, as if reading Nico's thoughts, "until the war against Gaea. I have to say even I was amazed to see the Romans and the Greeks fighting together as allies. I have seen many wars in my existence, but this was the first time I saw two different pantheons working together so flawlessly …Not that it did them any good, seeing as they all got wiped out in the end."

"…Why am I here?" he asked quietly, his energy sapped from the information overload. "Why am I alive again? Did you bring me here just to show me all of this? What for? Why…?"

He didn't want to be alive again. He was fine with being dead. He had welcomed it, in fact. He was a Son of Hades. He'd been to the Underworld plenty of times. Death was nothing new to him.

Death was peaceful, easy. Death meant that he could leave all of his life-associated worries behind. Death meant that he could see his mother again.

More importantly, death meant moving on… moving on from life, from love, from everything that was hurting him. It was his chance at a fresh start.

"You're here," the boy, "because it's easier to convince you if you saw the consequences for yourself."

"…Convince me of what?" he asked slowly.

"We're trying to convince you to travel back in time and prevent this," he gestured to the ruined land around them, "from happening."

"…What?" Nico asked just as slowly, as if he wasn't sure of what he'd heard. They wanted him to travel back in time (he didn't even know that was even possible) and do what? But, "Why me?"

Really, why? What could he do to stop the apocalypse? He was no powerful hero. Sure, he was one of the children of the Big Three, but he was nothing like the heroic Percy Jackson and Jason Grace. He wasn't a leader like Thalia and it was no secret that everyone liked his sisters more. He was just Nico, the dark and creepy-

"-Son of Hades," his thoughts were unexpectedly finished by the ghost-lady. "It is because you are a Son of Hades that we chose you."

Okay, let's add 'getting chosen for an impossible quest' to his personal List of Reasons Why I Hate Being a Son of Hades.

"Hey, don't look at us like that," Chronos said gruffly. "It's not like we decided to choose you on a whim. It took us three years to make our choice."

"How would being a Son of Hades make anyone think that I have any chances of stopping the world from ending?" he asked incredulously.

"We have many other reasons on why we chose you. It's not just that," the boy said. "You're also Hades' most powerful offspring to be born in the past five hundred years."

"I'm still not getting it," he snapped. What they were asking him to do was beyond anything he had ever done in his life. The impossibility scale of this beat 'Surviving Tartarus' by a few dozen points, at the very least. "And Hazel could be a lot stronger than I am, if she had more time training her powers," he defended his sister.

"But her powers aren't the same as yours," the boy opposed. "Your powers control the death aspect of Hades' powers. It has to be you."

"That… being," the ghost-lady said, having a hard time finding the right pronoun to describe the destroyer of the world, "has a very powerful ability." Naturally, she didn't tell him what this great and powerful 'ability' was specifically. But, maybe Nico should count himself lucky. This was the most information he'd been given for any quest he'd ever been on. "As a Child of Hades with influence over death, his powers cannot influence you so easily."

"What exactly is this 'being'?" Nico asked. They could at least tell him that, can't they?

"This being was once a human," she said. "Now he could be called nothing else but a monster. He lost his humanity when he stole a weapon of the gods."

Wow, he'd heard of gods losing their stuff or having it stolen, but it was usually another god (or a demigod) that's to blame. He'd never heard of a normal human pulling a stunt like that.

"Well, technically what he did couldn't be considered stealing since that thing didn't have an owner anymore," the boy began to explain. "After its original owner faded, the weapon lost its original form and became nothing more than a deformed tool with a lot of divine power. A human somehow managed to find a way to absorb all of that power into his body and use it for his own purposes. But he soon learned that a human's weak body could not withstand such immense power for long. So, he somehow found a way to turn himself immortal which consequently lead to him losing his humanity."

"This has nothing to do with the Greeks or Romans, does it?" Nico asked. "The god this weapon belongs to is probably from some other pantheon, right?" he guessed.

"Yes," the woman confirmed.

"Then what do you need me for?" he asked. "Didn't he," Nico pointed to the boy, "just say that the different pantheons weren't supposed to meddle with each other's' affairs? Why can't those gods ask one of their followers or champions to stop this guy?" he tried convincing them.

"But there are no followers!" the woman exclaimed, like she had repeated this argument hundreds of times already. "There are no champions and there is no god!"

"Wha-?"

"The gods of my pantheon have long since faded," the woman said devastatingly. "We don't have demigod children to rely on. No one believes in the gods anymore. And with no one to believe and rely on us, we lost our power and disappeared with the dawn of the New World. With the god's end, the weapon lost its master. It is no surprise that a mere human was able to get his filthy hands on it so easily.

"There is no one else," she said desperately. "You are our- the world's only hope!"

Yeah, no pressure or anything…

And she said 'we' and 'us'… so she's…

"First off, technically, I said 'no divine being was allowed to meddle'. And I did add that it all changed since the Greek and Roman pantheons worked together in the Giant War. Second of all, you see, we'd love to get someone else for this job, if we could," the boy said. "I mean, you don't exactly look like the most reliable demigod in existence." He kicked Nico's skinny frame to prove his point. "But, the problem is we can't.

"The gods of her pantheon are all either dead or dying," he said as he – rudely – pointed at the woman. "Because of the blood flowing through your veins, you're the only one who can come into contact with this weapon without disintegrating." Nico's throat went dry at the mental image that description brought. "This means, you're the only one with a chance of extracting the weapon from him."

Nico took a few long moments (and deep breaths) to absorb all of this.

So someone named Kronos and a goddess from another pantheon (he was still wrapping his head around that) had somehow brought him back to life three years after his death and they tell him that they want him to return to the past to prevent the end of the world…

Naturally, Nico had a lot of questions to ask.

"Why are you asking me?" he asked the younger looking boy. "I thought you hated demigods, especially after all the stuff that's happened in the last Titan War."

The boy blinked in confusion for a few seconds before realization dawned on his face. "Oh!" he exclaimed. "Son of Hades, I'm afraid that you're mistaking me for someone else. I am Chronos, the primordial god of time," he clarified, "not Kronos, the Titan lord of time. Unlike the Titan Kronos who has the power to influence time, I am the personification of time itself."

Nico blanched. A primordial god? Like Gaea?

"…Okay," he said slowly. Deep breaths, Nico. You're a demigod, you've dealt with the impossible and unlikely hundreds of times before. Just remember to take deep breaths. "And you are?" This time he asked the woman.

"Someone who wants to prevent the world from ending," she answered evasively.

Alright, then. "Are you guys the only ones in on this?" Nico asked. "Do any of the other gods – Greek, Roman or otherwise – know about this plan?"

"Chaos knows," not-Kronos answered without hesitation. "Other than that, no one but us has any knowledge of this. When you return to the past, unless you do anything drastic, the other gods won't be able to identify anything out of the ordinary about you."

"Next question," Nico said. "If I decided to do this," (He probably will, but they didn't need to know that yet), "and go back in time then does mean that I'll be able to change-?"

He hadn't even finished the question before the Greek primordial cut in. "You're only objective is to prevent the world's destruction," he said sternly. Then, he sighed, "Whatever you decide to do after that will be your choice."

Nico's mind whirred. There were a lot of things he wanted to change, so many disasters he wanted to prevent. If he could-!

"However," the boy interrupted Nico's thoughts. "You should know that Fate cannot be altered without a price. By just sending you back, we would change the lives and Fates of many people," the boy's expression turned grim, as if he could currently see exactly what the consequences of this were. "And not all of it will be for the better.

"Keep in mind that some things are meant to happen," he continued solemnly, "for better or worse."

Nico gulped.

"Besides" he said in a slightly lighter tone. "We won't just be sending you to the past, we'll also be sending you to London, where everything began," he revealed. "London is also where that being conducts most of plans. It will be easier for you to keep track of his actions if you were in London instead of America."

Okay, Nico had to admit that although it made sense to do that, it would also make it very hard for him to make the changes he wanted if he were in a different country.

"In London, you will meet someone with deep ties to that man and his plans," the woman said "That is as far as our influence can reach. Everything else that comes after that will be up to you."

"Before you ask any more questions," Chronos cut in. "What have you decided?"

Nico knew what Chronos was asking.

"Will you do it, Son of Hades? Will you return to the past and save the world?"

Nico's decision had been made for a while now – since he opened his eyes and saw the destruction that lay around him.

"I'll do it."

Sure, Nico would be the first to say that this world wasn't perfect – not with the kind of gods that were currently ruling it – but that didn't mean he wanted to see it end.

Nico took another look at his surroundings.

He would do whatever it took to prevent this. Even if he ended up failing, he wanted to at least try.

The translucent woman smiled.

He would do everything he could to save the world. He had to. After all, he lived in this world. And so did Hazel and his father… Percy too.

He didn't want any of them to die.

Chronos let out a relieved sigh and grinned.

"Then, what are we waiting for?!" Chronos exclaimed excitedly in an obviously fake British accent. "Come on, no more dilly-dallying! You've got a cab to catch!"

Nico passed out.

xXXx

When Nico woke up, he heard blaring horns all around him. He felt hard tarmac against his palms and knees and his head felt like something hard and heavy had rammed into it.

Then, something hard and heavy rammed into his side.

And Nico passed out again.

xXXx

A/N: Quick question, and THIS IS IMPORTANT, in America, if Percy's birthday was in August and Nico's in September on the same year, would they both be in the same grade?

I REALLY NEED TO KNOW THIS BEFORE I POST THE NEXT CHAPTER.