Masamune Izumi, a high school student and aspiring light novelist who is only 15 years old, is the protagonist of the story. However, Masamune merely writes the text for the light novels; his illustrator, "Eromanga-sensei," is responsible for their incredibly pornographic illustrations. Masamune believes that this is just another disgusting, perverted otaku, but no one has ever seen him. Sagiri Izumi, his younger sister, who is 12 years old, presents him with very new issues. Although they are not biological relatives, the two have been living together in isolation under the same home for the past year for various reasons. But ever since, she has isolated herself in her room and ceased attending school. Masamune now requests that she leave her room once more. It transpires that Sagiri is also "Eromanga-sensei," nevertheless. In addition to the pandemonium that develops between the two, a well-known light novelist makes an attempt to steal "Eromanga-sensei" for her own works.
