Rise of an Assassin

A boy is reincarnated in a society based around strength, where big brutes are seen as the perfect human and people with weak bodies like the boy are trash, seen as nothing but something to abandon.

The boy, indignant about his circumstances, makes a deal and sets on his way to become strong.

(Author note: The character won't be physically weak for too long, it's just something that will be pretty big at the start.)