Why is this boy loyal to this girl and hard to intimidate?

Kid55151
Hello! I am a 17 year old boy who is currently attending highschool.

Currently, an eccentric introvert is my highschool classmate. He is also a martial artist. Why is he loyal to the weird theater girl and not to the popular kids despite the popular kids being popular? He is defiant towards the popular kids when it comes to protecting her.

This eccentric introvert listens to the weird theater girl but is rude to the popular kids when they try to make him do something.

Against the popular kids, he isn't invincible because a gang of male student athlete popular kids beat him up when he fought them but he seems indomitable towards the popular kids in that the popular kids such as the athlete kids, the cheerleaders, etc. can't seem to make him submissive to them or intimidate him.
Why is this boy loyal to this girl and hard to intimidate?
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