Izumi Masamune is a high school student who loves writing light novels. Having no artistic skill himself, Masamune always gets his novels illustrated by an anonymous partner using the pen name Eromanga Sensei who, like the name suggests, draws 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 Izumi Sagiri. 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 has been Sagiri all along, their sibling relationship quickly leaps to new levels of excitement, especially when a beautiful best-selling shoujo mangaka enters the fray.