My Big Sister Lives in a Fantasy World: Volume 4: The Melancholy of the High School Girl Light Novel Author?!

Yuichi's not-very-restful summer vacation came to an end, and the new school term isn't looking much better. Immortal demons are trying to kill him, his new teacher is a superpowered sociopath, and all kinds of bizarre events are happening around the school. What does Kanako's new novel have to do with the bizarre goings-on at Seishin High? Once again, it's up to the world's strongest little brother, and his highly delusional sister, to find out!