"Eromanga Sensei" centers around Masamune Izumi, a high school student and aspiring light novel author who writes under the pen name "Eromanga Sensei." After the death of his stepmother, Masamune takes on the responsibility of caring for his reclusive younger stepsister, Sagiri Izumi, who has not left her room for over a year. Sagiri spends her days drawing illustrations for light novels, unbeknownst to Masamune, who has been collaborating with her online under the alias "Eromanga Sensei," assuming the illustrator is a perverted middle-aged man.

The narrative unfolds as Masamune discovers Sagiri's true identity as his illustrator. This revelation forces the siblings to confront their strained relationship and work together more closely. Sagiri, who initially resists interaction, gradually opens up to Masamune, and their collaboration deepens. The story explores their evolving dynamic, blending themes of family, creativity, and personal growth.

Supporting characters include Elf Yamada, a rival light novel author who becomes infatuated with Masamune; Muramasa Senju, a talented but eccentric writer who competes with Masamune professionally; and Megumi Jinno, Masamune's childhood friend and editor, who provides guidance and support. These characters add layers to the narrative, introducing conflicts, rivalries, and comedic moments while contributing to the central themes of artistic collaboration and self-discovery.

The series balances slice-of-life elements with lighthearted humor and occasional dramatic undertones, focusing on the challenges of creative work and the complexities of familial relationships. Through its exploration of the light novel industry and the personal struggles of its characters, "Eromanga Sensei" presents a story that intertwines professional ambition with emotional growth.