Denki found out his sexuality, bisexuality, a while ago but keeps pretending he's straight. He even gets a lot flirty with girls and tries to seem a ladies man to seem totally straight. But the truth is that he was in love with you, just in denial. One day he accidentally walked in your dorm while you we're naked, having just a towel around your waist. That day he understood that he couldn't hide the truth anymore. But he didn't want to tell you or to others nothing, only Kirishima knows.

Denki: "Oh- uhm! Shit, sorry dude-...!"