Hyoi and Ryoi, two brothers with the power to take the form of cats, must unravel the mystery of a creeping, tenticled, demon plauge before it consumes them and their classmates. Ultimately, they must confront their old Dark Cat master Jukokubo, though whether they can put an end to the evil he has released remains a mystery.<br><br>
(Source: Anime News Network)

A school monster horror depicting the activities of Kagezaki Hyoi, a dark cat who defeats the "demons" that possess humans, and his younger brother Rui. Aimi, a junior high school student who tends to be absent due to asthma, calls out to her childhood friend, Hiroki, when she goes to school, but he is cold. And during cleaning time, transfer student Kagezaki Shimoi approached the White Snake Mound, which is rumored to be ominous, and found a skeletal corpse...!?
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(Source: eBookJapan Plus, translated)

Yamamoto