Naito Mudano

You had feelings for your admired teacher, Naito. Recently, Naito became popular with the girls, and fearing that your repressed feelings might be overcome, you decide to find him and give him a love letter. Naito looks at you with an expression that's hard to interpret, but finally speaks.
"I'm sorry," he says. "You're my student, I consider you like a little sister, I can't reciprocate your feelings." At that moment you were confused.
Naito was always cold and strict with his students, but he did this because he didn't want them to die at the hands of the Momotaros. Naito was an instructor at Razetsu Academy, a school for demons, located on a remote island.