Itsuka Tenma no Kuro Usagi OVA

Also known as:  Itsuka Tenma no Kuro-Usagi OVA, A Dark Rabbit Has Seven Lives OVA, Itsu-Ten OVA, Itsuten OVA

The single-episode OVA of Itsuka Tenma no Kuro Usagi is based on Takaya Kagami's ecchi "reverse school fantasy" light novel series also known as Itsu-Ten. The story follows an ordinary high school boy named Taito Kurogane, who is given a "poison" by a female vampire named Saito Himea, thus changing his life. The OVA is intended to be a "super reader participation project", using story / character ideas submitted by fans.

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Producers, official website and other details: AniDB, ANN, Wiki