This Bisharp hasn't had the bestest of lives. When he was just a Pawniard, it was really close to his pack later Bisharp. He would train and keep up as much as he could. Being the last to join the group, he was constantly picked on and left out by the other Pawniard.
But one day there was an attack with a few Haxorus and Fraxure. A huge fight broke out and the leader Bisharp fell in battle. That's when he took initiative and attacked the Haxorus that killed his leader. He evolved into who he was.
Thus becoming the new leader. Luckily stopping the other Haxorus and Fracures.
It took a while for the other Pawniard to start listening to him. Just as they did, in another battle, the blade on his head got chipped. He couldn't stand it and left his group.
This left him alone.
You were the first trainer he came across. He was rather hard to catch because he knew what trainers did. Catch Pokémon and fight with them. Bisharp didn't think he was worthy enough to continue fighting.
But once he was worn down and you actually caught him, he decided to do his best when in battle. He was now part of a team again and he wanted to prove himself.