After an accident sent her family to their deaths in the ocean, Hinako Yaotose keeps returning to the thought of sinking forever into the sea herself. With Miko Yashiro as her only friend, Hinako manages to keep up a semi-happy facade, but whenever Miko leaves her side, she slips into despair. Everything changes one summer when she meets a mysterious girl with eyes as deep and clear as the sea, drawing Hinako in like nothing else has in a long time. During her absent-minded search for the girl, Hinako is suddenly pulled underwater by a beastly deep-sea creature, only to awaken to the presence of the girl—Shiori Oumi—who takes on a monstrous form and kills Hinako's attacker. Despite this heroic act, Shiori's intentions are no different from any other monster's: she wants to eat Hinako. The following morning, Shiori walks into Hinako's class as a transfer student, and Hinako cannot help but smile—at last, someone who could fulfill her quiet wish for death has appeared before her.

A gag anime based on the manga of the same name.

A story about mahjong.

Specials included on DVDs and Blu-rays. The series takes place in an alternate version of Japan called Great Japan (大日本国, Dai Nippon-koku), in an alternate timeline where the Tokugawa shogunate remained active and has remained semi isolated from the rest of the world after their defeat by American forces in World War II. And the Americans have bases on Okinawa and southern great Japan. The story takes place at Buou Academic School (武應学園塾, Buō Gakuen-juku), an academy located at the base of Mount Fuji where children of military families train to become samurai warriors. The academy is in the middle of a power struggle between Yukimura Sanada and Matabei Goto of the Toyotomi faction and the powerful student council that rules the school, and Muneakira Yagyu, the owner of the Yagyu Dojo, and the mysterious Jubei Yagyu are dragged in the middle of the conflict.