Masamune Izumi is a light novel author in high school. His artist, known only as "Eromanga Sensei" is reliable but Masamune has never met him and assumes he's just a perverted otaku. Masamune's little sister is Sagiri, a shut-in girl who hasn't left her room for an entire year. She even forces her brother to make and bring her meals when she stomps the floor. Masamune wants his sister to leave her room, because the two of them are each other's only family.
One day Masamune discovers that Eromanga Sensei and Sagiri are one in the same. Further chaos erupts between the siblings when a beautiful, female, best-selling shōjo manga creator becomes their rival.
Keita has two older stepsisters, Ako and Riko, but since they aren't related by blood, they love him in a lustful way. After a mishap at school, Ako and Riko finally confess their love to him. Keita dislikes the thought of seeing them other then brother and sister, but as he tries to enter the same school as his sisters, he slowly becomes attracted to them.
A girl named Mitsuki Kanzaki lives with her step-brother Yuya after her mother remarries. One day, Mitsuki is possessed by the self-proclaimed spirit of a young girl, Hiyori Kotobuki. Hiyori (in Mitsuki's body) must fall in love with Yuya to move toward the "Gates of Heaven."