It could be that Percy is in Tartarus looking for a way to close a portal that Kronos is guarding. Kronos, weakened but still menacing, tries to bargain with Percy. He offers Percy power if he helps him escape Tartarus. Percy refuses, of course. Then they engage in a fight where Percy uses the environment of Tartarus, like the unstable ground and the strange creatures, to his advantage against Kronos.
In fanfiction, when Percy meets Kronos in Tartarus, Percy might be initially terrified. But he soon gathers his courage. Kronos might start taunting Percy, saying things like how he is a fool to come to Tartarus. Percy, in response, challenges Kronos' view of power and domination. They then start a battle of ideologies as much as a physical battle, with Percy arguing for the good of the world and Kronos trying to justify his past actions of trying to take over.
In fanfiction, when Percy meets Kronos in Tartarus, it could be a battle of wits. Percy has faced many challenges before and learned from them. Kronos, on the other hand, is cunning. Percy might try to outsmart Kronos by using the chaotic nature of Tartarus against him. He could lead Kronos into a trap where the very essence of Tartarus, like the rivers of fire or the howling winds, would weaken the Titan.
The first encounter between Annabeth's friends and Percy in fanfiction can vary greatly. It could start with a simple introduction in a common place like Camp Half - Blood. Annabeth's friends might be friendly right away, asking Percy about his quests and his life outside the camp. Or it could be in a more dangerous situation where they have to rely on each other immediately. In this case, they might not have time for formalities and quickly start working together, getting to know each other's strengths and weaknesses as they face the threat at hand.
Maybe it's part of a plot to have Percy gain some sort of power or knowledge. In many fictional stories, a character has to go through great pain and suffering before emerging stronger or wiser. The torture in Tartarus could be a way to set up this transformation for Percy.
Perhaps he could make an alliance with some of the less hostile creatures in Tartarus. There might be beings who are also tired of the chaos and want to help Percy in exchange for something, like a promise to free them from Tartarus if he ever gets the chance. Percy is known for his charisma and ability to make friends, even in the most unlikely situations.
The encounter between Percy and Nico at the Lotus Hotel in the fanfic might be a turning point for both of them. At first, they might approach each other with a bit of suspicion. But as they start to communicate, they discover that they can learn a great deal from one another. For example, Percy could teach Nico about loyalty and friendship in a more direct and open way, while Nico could show Percy the importance of understanding the darker aspects of the world. As they explore the hotel, they might face some minor challenges together, like getting lost in the maze - like hallways, which could further strengthen their connection.
The first encounter could be quite awkward. The Avengers, being a group of superheroes, might seem intimidating to Natasha's family. They could all be standing around, not really knowing what to say at first.
One possible consequence is that the demigod world would be thrown into disarray. Percy has been a key figure in maintaining some sort of order, and with Kronos in control, that order would be shattered. Another consequence could be that the Gods would be in a real bind. They already had trouble with Kronos before, and now with him in Percy's body, it would be much harder to fight him.
In fanfiction, Percy could become a champion of Kronos due to a complex web of factors. It could start with his disillusionment with the Olympians. After all the battles he's fought for them, if he sees no real change in how they treat demigods or the world in general, he might be open to an alternative. Kronos, being a master manipulator in these alternate stories, could offer Percy power and a chance to truly make a difference. Also, Percy's relationships could play a role. If someone he trusts sides with Kronos and convinces him, or if he's in a situation where he has no other allies and Kronos offers support, he could end up in that role. But these are all departures from his original character in the official Percy Jackson series.
Well, one possible consequence could be that Percy gains an immense amount of power. Kronos was a very powerful Titan, so Percy might become nearly invincible. He could also face some internal struggles as Kronos' essence might try to influence his mind and actions.
One possible storyline could be that Percy is tricked into betraying Tartarus by some dark force. Maybe they use his friends as hostages or manipulate his mind. Another could be that Percy believes he's doing the right thing in betraying Tartarus, but later realizes it was a huge mistake and has to face the consequences. For example, he might face the wrath of Tartarus' minions or lose the trust of his allies.