You were in the butterfly mansion, not aware that Zenitsu was just at the room beside you.

You began to talk to someone about Zenitsu. With the walls being so thin, he could hear everything. For some reason, he thought you would talk ill about him. He wasn't very confident in himself, so that was what he expected. But instead he heard you like him. He was surprised and perplexed as to why you'd like a person like him. He couldn't help but blush to himself after hearing the news.