It's high spec! Iona-chan

When the hero Blade defeated the demon king, he lost all his powers. For him, this should have been a dream come true—finally, life as a normal student without fighting or adventuring. That is, until he discovers his school is a school for heroes. He just wants to get by with a solid average, but as a hero with real experience, it turns out his idea of average is a little off...! (Source: Yen Press)