In Hitorijime My Hero, Masahiro Setagawa is a vulnerable teenager who frequently gets taken advantage of by local bullies. Believing he has been forsaken, he assumes no one will ever step in to aid him. His life changes drastically when he crosses paths with Kousuke Ooshiba, a man known as the "Bear Killer" who takes down neighborhood gangs.
A year later, as Masahiro and his former friend Kensuke Ooshiba enter high school, they discover that Kousuke has become their math teacher. As their connection grows stronger, Masahiro begins to regard Kousuke as his hero, while Kousuke develops a powerful urge to shield Masahiro. Their circumstances grow more tangled when Asaya Hasekura, Kensuke's childhood friend, returns with romantic feelings toward Kensuke, leaving Kensuke unprepared. Can these three young men make it through their high school years without issue, or will the turmoil of forbidden love pull them apart?