He is the vice principal of the Academy and was enjoying a cup of tea during the new semester when Kaori Saeki, one of the teachers and character of previous Bible Black series, offers to take him to a secluded cabin on the Academy grounds. She then gives him some tea but laced it with a potent drug.
At the cabin, Oshima is taken through an underground tunnel and finds six female students engaged in occult activity. The drug kicks in and Takeshi engages in an orgy while admitting he always liked Saeki. Saeki takes a golden cup and fills it with Takeshi's semen for occult purposes. The sex Takeshi endured with the cultists causes a demonic entity to possess him in the form of a symbol. The demon turns him into a pawn to the main villain Jody Crowley. Outside Takeshi makes an evil grin before being hit by a truck. In the hospital, Takeshi flirts with the nurse Eri Haruda and the two kiss. Before the two have sex, the symbol appears on Takeshi's forehead causing the demon to take over and violently rape Eri.After that, Takeshi finds Aki Ichikawa to find the Spear of Longinus fragment in her body. Raping her as well, Takeshi stabs Aki with a knife before Naoto Yamanishi knocks him unconscious. Knocked out, the symbol disappears from his forehead, hinting that the demon left. What happened to Takeshi afterwards is unknown but it's likely his life is ruined.