Masamune Izumi is a high school student also working as a light novel author. He works with a mysterious illustrator who draws really erotic art for his light novels. In the midst of trying to deal with school and his shut-in sister, he discovers the identity behind this Eromanga-sensei!

Masamune comes home from his trip, and Sagiri is happy to see him return. They now await their new novel to go on sale. On the day of, an “Izumi Masamune Faire” is held in a store in Akihabara. While Masamune and Sagiri “explore” the area, they share their stories of how they got into writing novels and illustrating.

Masamune and Sagiri’s new work, "Sekaimo: The World’s Cutest Little Sister" is now on sale. Sagiri continues to stream from her room wearing a mask as always, and declares the curtain rising on a "Festival".