Sagiri Izumi and Masamune Izumi were step-siblings a year ago. However, the tragic loss of their parents shatters their new family, causing Sagiri to become a shut-in, cutting her off from her brother and society. Masamune earns a living as a published light novel author while caring for what's left of his family. There's just one problem: he's never met his celebrated illustrator, Eromanga-sensei, who is famous for sketching the most obscene erotica. He discovers, after a humiliating series of circumstances, that his very own young sister was his companion the entire time! Masamune and Sagiri must now tackle the light novel industry together as new characters and difficulties emerge. Eromanga-Sensei covers the evolution of their romance as well as their battle to achieve success; andas Sagiri slowly grows out of her shell, just how long will she be able to hide her true persona from the rest of the world?