Perhaps Percy sacrifices himself to save his friends. In Tartarus, if his friends are in a life - threatening situation, Percy, being the selfless hero he is, might choose to give up his own life to ensure their survival. For example, if there was a powerful curse or a trap that could only be stopped by one person taking it upon themselves, Percy would be the one to step forward.
It could be that Percy succumbs to the dark and corrupting influence of Tartarus itself. The place is filled with negative energy and despair. Over time, this could break his spirit and weaken him physically until he is no longer able to fight, and ultimately die.
One possible scenario could be that Percy is overpowered by the various monsters in Tartarus. Maybe the sheer number of foes like the giants or the more terrifying creatures there are too much for him to handle, leading to his death.
Another scenario could be that Percy is forced to endure extreme environmental conditions in Tartarus. The place is known for its intense heat, toxic fumes, and jagged terrain. He might be made to traverse through burning lava fields or climb sheer cliffs while being constantly weakened by the poisonous air, all of which would be a form of torture.
One possible scenario could be that Percy sacrifices himself to save Annabeth from a powerful and deadly monster. Maybe a huge and ancient sea creature that only Percy can hold off long enough for Annabeth to escape, but at the cost of his own life.
In a 'Percy Jackson Dies' fanfic, one possible scenario could be that he sacrifices himself to save his friends during an epic battle against a powerful new enemy. Maybe a horde of monsters that are immune to his usual powers overwhelm him while he's trying to buy time for his friends to escape.
One possible scenario could be that Percy sacrifices himself to defeat a powerful enemy. Maybe he uses his powers to hold off a huge monster that is about to destroy Olympus and in the process, he gets fatally injured and dies. Another could be that he is betrayed by someone he trusts, which leads to his death. For example, a demigod who is jealous of Percy's popularity and powers might make a deal with the enemy and set Percy up.
One interesting scenario could be Percy and Annabeth finding a hidden, powerful weapon in Tartarus that gives them an edge against the monsters there. Maybe it's a sword that can cut through the very fabric of Tartarus's darkness.
Another scenario could be that Gohan contracts a deadly and incurable disease in the fanfiction world. Despite the efforts of his family and friends, including the use of any available advanced technology or magic, he succumbs to the illness, leaving everyone in mourning.
One possible scenario could be that Luffy sacrifices himself to save his crew during a major battle against an extremely powerful enemy. He might use all his strength and energy to protect them, and in the end, it's too much for his body to handle.
Maybe there's a powerful, ancient monster that Percy battles single - handedly to keep Artemis safe. The monster could be something like a Titan that has been awakened and is far too strong for Percy to defeat alone.
One scenario could be that they are facing a powerful monster. The monster is about to strike Annabeth, and Percy jumps in front of her at the last moment, taking the fatal blow. Another possibility is that they are in a dangerous situation like a collapsing building or a sinking ship, and Percy uses his powers to ensure Annabeth's escape while he stays behind and perishes.
One possible scenario could be that Edward sacrifices himself to defeat a powerful and final enemy. He might use up all his alchemy knowledge and power in one last, desperate attempt to save the world, and his body just can't take the strain.