This"sibling amorous humor" revolves around Masamune Izumi, a light novel author in senior high school. The little sister of masamune is Sagiri, a shut-in girl who has never abandoned her room for an entire year. She forces her brother when a floor stomps to bring and make her meals. Masamune wants his sister because the both of these are the only family of each other. Masamune's novel illustrator, pen name"Eromanga," draws extremely perverted drawings, and it is very dependable. Masamune had never met his illustrator, also guessed he was simply a otaku. However, the truth is shown... his"Eromanga-sensei" is their own younger sister! To increase the madness that contrasts between the sisters, a beautiful, female, best selling shoujo manga founder becomes their rival!