An Incubus (夢魔) is a low class devil, who shows up in dreams as the opposite sex, offering pleasure and corrupting people.
As part of a training to capture a released incubus, Matsugo and his class received a dream consolidation incense, that connects each other’s dreams, where they must search the creature who slips into anyone’s dream. Matsugo put one in Rinne’s room without his permission, which causes Rinne dreaming of Sakura turning into Matsugo. As that tiny creature wore the emblem of the Shinigami Elite School, Renge was able to identify it, so Rinne went to Matsugo’s house along with Sakura, Tsubasa and Renge. After learning about the training, Rinne had no choice but to fall asleep and endure Matsugo in his dream to find the creature. Sakura, Tsubasa, Renge and Anju would also be involved having their own dreams, and after enduring a lot of frustrating situations, Rinne managed to punch the incubus which had landed on his face, thus end his hell.