The story centers around high school student Masamune Izumi who loves writing light novels. Having no artistic skill himself, Masamune always got his novels illustrated by an anonymous partner using the pen name "Eromanga Sensei", who is known for drawing questionably perverted images despite being extremely reliable. In addition to balancing his passion and school, Masamune is also stuck with taking care of his only family member—his younger sister Sagiri Izumi. A hikikomori by nature, Sagiri shut herself in her room for over a year and constantly bosses Masamune around despite his attempts to get her to leave her room. However, when Masamune inadvertently discovers that his anonymous partner had been Sagiri all along, their sibling relationship quickly leaps to new levels of excitement, especially when a beautiful, female, best-selling shōjo manga author enters the fray.