In this type of fanfiction, Darkseid could be a major antagonist. He is one of Superman's greatest foes. If he discovers that there is a 'son of Superman' in the world of Percy Jackson, he might try to invade that world to either capture Percy or use the power of the demigods for his own evil purposes. Also, some of the traditional demigod villains like Ares might also oppose Percy more strongly now. They might be jealous of his new powers and see him as a threat to their status among the demigods.
The main antagonists could be the Titans. They are powerful enemies in the Percy Jackson universe already. Now that Percy has Superman - like powers, they might see him as an even greater threat to their plans of overthrowing the gods. So, they would do everything in their power to stop him.
Perhaps Hades could be an antagonist in this fanfiction. He is often at odds with Percy in the original Percy Jackson stories. Now with Percy having Superman - like powers, Hades might feel that Percy is getting too powerful and could potentially disrupt the balance in the underworld. Also, the villains from Superman's world like Metallo could be brought into this story. Metallo, with his kryptonite - based powers, could pose a serious threat to Percy if he manages to find a way to counter Percy's demigod and Superman - like abilities.
A practical answer is Chapter 225, because it turns the idea into a concrete scene. The chapter opens with When Zhao Lang's devastatingly handsome face appeared, all six people..., adds pressure through Alright, it's about time, let's officially get started., and ends on Which big shot is.
Look to Chapter 223 for the clearest answer. It begins with So, for the first time, Jiang Yan, who had always styled himself as the..., keeps building through My good little sister, I'm begging you, help me figure out how to avoid..., and lands on The damned Jiang Li was tricking him again!.
Chapter 222 is the strongest chapter-level answer because it starts from How come they're even live streaming in a reality show?! and follows through on She was certain and sure that she saw scheming in them..
Chapter 252 is the strongest chapter-level answer because it starts from In fact, Jiang Yan's shirtless appearance this time was entirely Jiang... and follows through on Aren't these few days supposed to be solely my spotlight time?" Camera....
If you want the clearest chapter reference, go to Chapter 232. Early on, But soon, she suppressed this strange feeling and slowly began to speak,...; later, the chapter leans on I'm the oldest, so I should get this chance!" "Get lost, I'm the youngest....
If you want the clearest chapter reference, go to Chapter 202. Early on, Jiang Li couldn't believe it, "Just to take a picture?" "Yes, just to take...; later, the chapter leans on If just taking a picture could earn thirty points, it was indeed worth it..
The best chapter pointer here is Chapter 254, "Madwoman! She is definitely a madwoman!". It opens with Just when everyone thought that Jiang Yan wouldn't last long and would... and closes on A Jiang Li whose head was only filled with books and who never joked or....
Chapter 252 is the strongest chapter-level answer because it starts from In fact, Jiang Yan's shirtless appearance this time was entirely Jiang... and follows through on Aren't these few days supposed to be solely my spotlight time?" Camera....
Look to Chapter 224 for the clearest answer. It begins with Jiang Li, ranked number one, was directly taken by the staff to an elegant..., keeps building through The building had two floors, decorated in an elegantly serene manner,..., and lands on After all, the fans of Su Yinwan next door had.
If you want the clearest chapter reference, go to Chapter 214. Early on, Director Sun fell silent for a second.; later, the chapter leans on You know, you're right." Jiang Li: "...." Now, even the audience began to....