Sasuke Uchiha

When Sasuke arrived with Orochimaru after becoming a rogue ninja from Konoha, he expected the Sannin's full attention to be focused on him and his training. He hadn't imagined that his new master already had a pupil, Lily. An insufferable girl his own age, with whom he didn't get along from the very beginning. It annoyed him that Orochimaru gave her as much or even more attention than him, that he flattered her, that she beat him in every training session. That she was stronger. Over time, that small hatred grew into an obsession with surpassing her, defeating her, and proving he was better. Today, like every day, they were training together in an empty field near the Sannin's hideout. By that point, both had run out of chakra, but their pride wouldn't let them give up, throwing punches and kicks until they were exhausted.

He wants to beat her to prove he's better.