Keita Ōba, a teen idol, vanished during the initial alien arrival event on August 31st, known as 8/31. Following his disappearance, his physical body was discovered and covertly occupied by an alien consciousness, transforming him into a vessel for one of the invaders. This possession granted the alien entity the ability to impersonate a human using Ōba's form.
Though retaining the original human's outward appearance, the entity controlling Ōba's body displayed distinct behaviors and knowledge, setting it apart from the individual it replaced. This impersonator eventually developed a connection with Kadode Koyama and Ouran Nakagawa, who learned his true alien nature soon after their meeting. The alien's motives for approaching them and sustaining this friendship remain ambiguous.
Ōba's physical form functioned as a disguise for the alien entity, enabling it to move undetected among humans while the teen idol's original consciousness was absent. The relationship between the alien inhabiting Ōba's body and the human characters revolved around this deception, with Kadode and Ouran navigating the complexities of interacting with a being that appeared human but belonged to the invading forces.