Complex sentence: A fellow student, Yoshizaki, mentions the appearance of ghostly looking people around campus and explains his theory that the place where souls go to is full and that they have begun to invade the physical world.
Split into simpler sentences: A fellow student, Yoshizaki, mentions the appearance of ghostly looking people around campus. Yoshizaki explains his theory that the place where souls go to is full, and the ghosts are invading the physical world.