In this fanfic, Percy could make use of his ability to heal quickly. He could take some hits from Thanos but keep coming back stronger. He might also use his wits. He could figure out the weaknesses of Thanos' weapons and armor. Then, he could use his powers to target those weaknesses. For example, if Thanos' gauntlet has some sort of energy source, Percy could use water to short - circuit it. Also, his loyalty to his friends could give him an extra boost of strength and determination to defeat Thanos.
Percy could use his knowledge of Greek mythology against Thanos. For instance, he might use the power of the gods in some way. He could call upon Poseidon to create a massive earthquake or tsunami. And since Percy has a lot of experience fighting monsters, he could use his battle - tested tactics. He could feign retreat to make Thanos overconfident and then strike back with a powerful counter - attack.
Annabeth could definitely be one of his main allies. Her intelligence and strategic planning would be invaluable in a fight against Olympus. Also, Grover might be there, using his skills as a satyr to gather information and support from other nature - related beings. Some of the less - well - known demigods from Camp Half - Blood could also join in, seeing Percy as a chance for a new order.
In such a fanfiction, perhaps Percy could use his unique powers in new and unexpected ways. He might gain the support of some unexpected allies among the demigods or even some minor gods who are tired of the Olympian regime. This could lead to a large - scale battle where Percy's strategic thinking and combat skills are put to the ultimate test against the might of Olympus.
Another possibility is that Percy discovers some long - forgotten weakness of Zeus. In the world of fanfiction, the author could create a scenario where Percy stumbles upon an ancient prophecy or a hidden secret about Zeus. This knowledge could give Percy the upper hand. He could then use his wits and his powers to exploit this weakness and defeat Zeus.
In a fanfic, Percy Jackson could defeat Thanos with his water powers. He might use the water around to create huge tidal waves and drown Thanos. Also, his speed and combat skills, which he has honed through many battles in his own world, could give him an edge. He could quickly dodge Thanos' attacks and strike back with his sword Riptide.
One challenge could be dealing with the child's past traumas. If the child has been through a lot, like being orphaned or facing monster attacks on their own, Percy would have to help them heal. He's not a trained psychologist, so it would be difficult for him to know exactly how to handle it.
Perhaps he has been exposed to some sort of deadly and unknown substance in the mythical world. This could be a new type of monster venom or a strange plant that he accidentally ingested. The substance could be attacking his body from the inside, causing his internal organs to bleed, and thus he throws up blood.
He could use chi for combat. Just like he uses his demigod powers to fight monsters in the original stories, he could incorporate chi to enhance his physical abilities. For example, using chi to increase his speed, strength, or agility during battles against new and powerful foes in the fanfic.
He could use it as an additional power source for his water - related abilities. Maybe chackra helps him control water in a more precise and powerful way.
Poseidon is a likely candidate. Since he is Percy's father in the original series, it would make sense for him to take a more active role in raising Percy. He could teach Percy all about the ocean, its secrets, and how to use his water - related powers more effectively.
One main theme is the clash of power. Percy, with his demigod powers, and Thanos, with the Infinity Stones, represent different kinds of power. Another theme is the struggle for survival. Percy is often fighting to protect his world, while Thanos has his own goals that threaten Percy's existence.