A Witch Joins.The Chairman meets the imprisoned Auroral Witch Mari Nikaido, who is suffering from magical amnesia, and makes her an academy student, hoping to use her as bait to draw out Valhalla. At the Academy the Chairman explains Lapis is a sword type relic and chose Taeru for his sword skills and has enrolled as a member of 35th Platoon under the alias of Takeru's sister. The Chairman orders 35th Platoon to guard Mari. Oka is outraged at having to keep a witch safe. Mari is outfitted with a Gleipnir necklace that will explode if she uses magic. Mari and Oka immediately fight with each other which gets worse as they compete in class, with Oka being more physically capable and Mari being more intellectually capable. Takeru doesn't care Mari is a witch and treats her like a member of the team. Mari expresses her desire to use magic to help people. Elsewhere Haunted, who is obsessed with Mari, recalls how Mari only agreed to work for him if he didn't kill innocent people, following which he had murdered academy students before erasing her memory and framing her for the crime. T stops Oka and Mari from fighting, only for Oka to realise Takeru is already calling Mari by her first name and the girls start a new fight now attempting to make each other jealous. Usagi enters them in a mock battle tournament against the other academy Platoons. Mari is told to live with Takeru (secretly the Chairman's plot to make her an easy target for Valhalla) and the jealous Oka insists on living with both of them to keep Mari from possibly seducing Takeru, but is terrified when Takeru's apartment appears to be haunted. An incident with Oka being scared by a ghost in the shower ends with both girls naked on top of Takeru, for which he is punished. Mari tells Takeru she is worried being a witch makes her too different from her human teammates. 35th Platoon struggle in the first round of the mock battle until Mari surprises everybody by using herself as a decoy, allowing 35th Platoon to win. Oka grudgingly admits they would have lost without her, which embarrasses Mari. Ikaruga is thrilled that Mari is the Tsundere member of the team. 35th Platoon celebrate their victory with the exception of Oka who delivers a report to the chairman, only to learn Mari was a member of Valhalla and was accused of murder.