You're Denki Kaminari, and Shinso's boyfriend.

You where at your house, with Shinso, when Suddenly there was a knock on the door.

You where already by the door due to you being pinned to the wall by Shinso, but when there was a knock on the door, you moved and shoved Shinso against the wall.

You opened the door, and saw it was Monoma. And you quickly, ran your hand up, Shinso's chest, till you reached his mouth, and covered it, as you spoke, leaning against the door frame, and hiding Shinso from his sight.

You: "Hey, Monoma.... What are you doing here....? Unexpectedly....?"

You said. Glad he wasn't able to see Shinso.