The manga received an Original Video Animation in 1991, which has the dubious honor of being one of the last works by Nikkatsu Corporation before its closure.
Not to be confused with Black Cat.
This series provides examples of:
- All Men Are Perverts: Miss Ogawa starts undressing and forcing herself on top of Ryoi to seduce him into telling her his true identity. Ryoi becomes visibly aroused out of his mind, and it's only thanks to his brother's interrruption (also because she sprouts a phallus-shaped demon out of her mouth) that he snaps.
- Ambiguously Human: It's never revealed whether the brothers are humans endowed with supernatural powers or supernatural creatures who can take human forms. Judging for the last line of the OVA, it seems they ignore it themselves.
- Animal Eyes: Hyoi has slit pupils, just like a cat.
- Animorphism: The main trait of the Dark Cats is turning into cats (apparently regular ones, telepathy aside). Reflecting their personalities, Hyoi becomes a black cat while Ryoi turns into a calico.
- Big Damn Heroes: Hyoi bursts into Miss Ogawa's office to save Ryoi.
- Body Horror: The demons take the shape of fleshy, tumor-like tentacled growths, some of them pretty phallic in shape.
- Break the Cutie: Aimi Koenji is put through hell.
- Cool Sword: The Dark Cat Sword used by the brothers. It can turn into a pendant.
- Devour the Dragon: Jukokubo eats Miss Ogawa (or rather, the demon she had become) to power himself up.
- Hair Intakes: Hyoi's hair resemble cat ears.
- I Have Boobs, You Must Obey!: Miss Ogawa undoes her shirt while she hypnotizes him. No doubt it helped.
- Heroic Sacrifice: Hiroki Koizumi ends with the demon menace by walking into the mass Aimi has turned into and telling her his true feelings.
- Immortal Immaturity: The brothers are implied to very old despite their entities, but Ryoi behaves much like the timid teenage boy he looks like, down to the Sacred First Kiss trope.
- I See Dead People: An ability of the Dark Cats, which is used by Hyoi to exorcise the ghost of a girl in the prologue of the OVA.
- Mind-Control Eyes: When interrogated by Miss Ogawa, Ryoi tries to use hypnosis on her to convince her he is just a regular student. Much to his surprise, it fails, and then it's Ogawa who hypnotizes him, revealing she is demon-possessed.
- New Transfer Student: The Kagezaki brothers play this to investigate in schools.
- Psychic Powers: Dark Cats can use mind control and a minor form of flight.
- One-Winged Angel: Jukokubo can abandon his relatively humanoid form and turn into a giant monster cat.
- Really 700 Years Old: Although they resemble middle/high schoolers in their human form, the brothers's age is implied to be very ancient. Hyoi mentions that they have been fighting Jukokubo for centuries.
- Sadist Teacher: Demon-possessed teachers like Ogawa and Iwata enjoy tormenting their students. It also includes Principal Nishimura, although in his case he is a sadist teacher without any need for possession, as he is actually Jukokubo.
- Shapeshifting Excludes Clothing: Played with. As seen when Ryoi transforms from cat to human in the OVA, he turns first into a nude human and then clothes appear on him, implying that the trope is played straight and that their clothes are materialized through magic.
- Sibling Yin-Yang: Hyoi, the older brother, is cool and professional, while Ryoi, the younger, is goofier and more emotional.