It could be that the hero was deceived or manipulated into joining. Or perhaps there's a deeper connection between the hero and the demons that hasn't been revealed yet. Maybe joining the demon army is the only way to save someone or something important.
Maybe it's for some hidden purpose or a unique mission. The hero might have seen an opportunity to achieve something greater by joining the demon army that others don't understand.
The reason could be that the hero has a change of heart and realizes that the demons aren't as bad as they seem. Or it could be a strategic move to gather intel and ultimately defeat the demons from within. Maybe the hero's sense of justice leads them to believe that joining the demon army is the best way to bring about real change.
Chapter 585, "He, Gu Yu, really has no bottom line!", is the clearest early answer because it turns Ji Yanbai's situation into a concrete plot event. The chapter turns that into something concrete by moving from The melee by the lake gradually subsided after an hour.
Chapter 641, "Congratulations to Jiang Li for Taking the Top Spot!", is the clearest early answer because it turns Ji Yanbai's situation into a concrete plot event. The chapter gives readers a real answer by opening on Surrounded by a sea of fire.
Chapter 551, "Who is Reciting "Student Rules"?", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. Early on, Other competitors were already in place, and Qi Tianyu was the last.... By the end, He would be much happier alone without the team!.
Chapter 450, "Your dear brother is making breakfast for you!", is the clearest early answer because it turns King Zheng's situation into a concrete plot event. The chapter gives readers a real answer by opening on And as he fell, he understood why Lao San had screamed so miserably.
Chapter 370, "Jiang Li, Thank You for Coming to Save Me", is the clearest early answer because it turns Mr's situation into a concrete plot event. It opens with He Yun's trial took place a week later, as scheduled.
Chapter 206, "Miss Su, Thank You So Much!", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Five minutes later, Xingxing led Ah Fu out of the room by the hand.
Chapter 222, "Oh, Miss Jiang Has Drawn It", is the clearest early answer because it turns Miss Jiang Has's situation into a concrete plot event.
Chapter 351, "Miss Jin Zhen Liu Suqing", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Yan: "....." How does someone manage to praise themselves with...
Chapter 211, "For Jiang Yan", is the clearest early answer because it turns Wen Jiaojiao's situation into a concrete plot event.
Chapter 636, "Beg Me", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on Uh..." Zhao Lang scratched his nose, feeling a bit embarrassed, "I...