Deimos no Hanayome: Ran no Kumikyoku revolves around high school girl, Minako Ifu, who has become the focus of the attentions of Deimos, former god of terror. For the forbidden love between him and his younger twin sister, Venus, the former goddess of love, he was turned into a demon by Zeus, and she was imprisoned in the Swamp of Death. In order to rescue Venus from her fatal punishment, he has to bring Minako, who appears to be her physical reincarnation, to the underworld so she can possess her body.

Adapting a chapter of the manga, this OVA is centered on Minako visiting the mansion of an infamous botanist in search and investigation of her missing friend.