Keito is a student of Yōkai Academy and a member of the Public Safety Commission, a police force made up of students that protect the school's peace. Her true form is a Jorougumo (a spider woman that has been known in Japanese legends).
Like many of the student police officers, she was ruthless and prone to employing violence, intimidation, and other immoral actions in order to further the Public Safety Commission's agenda, which was to extort Yōkai Academy's student body of money and impose their vision of law upon the school. This was a significant change from what they had initially been, which was as a militant group of students who ensured the safety of the school by intervening and resolving violent conflicts between the student body, since the school is host to a wide variety of monsters that may not get along.
Shortly after the defeat and exposure of Hitomi Ishigami, the Newspaper Club's activities had begun to irritate the Public Safety Commission. Keito reported their latest activities to the head enforcer, Kuyo, who decided to confront the Newspaper Club and attempt to intimidate them into submitting to the Public Safety Commission's demands and pay them the bribe.
This effort was impeded by Kurumu's indignant outburst, which prompted Keito to strike her with a loop of her spider silk. Kuyou immediately tasked her with monitoring the club's reaction. Despite orders from Ginei Morioka not to sell newspapers, Kurumu went ahead anyway, with Tsukune in tow. Keito quickly ambushed them, informing them of the previous year's defiance of the Public Safety Commission and their subsequent punishment, and then she proceeded to try to kill them.
Before she could so, Moka Akashiya intervened, which resulted in Tsukune being injured by Keito, who at this point had already revealed her true nature. Tsukune managed to remove Moka's seal, which released the Inner Moka. Moka proceeded to swiftly kicking Keito, which resulted in Keito being significantly injured and defeated. This event led to Kuyou's ill-fated alliance with Hitomi Ishigami, who wanted revenge against the Newspaper Club.
In the TV adaptation, Keito is still a member of the student police force, but her presentation and role are considerably different from her original counterpart. Here, she is seen in guise of a normal student who is in charge of a rival newspaper club, which is in fact backed by the Public Safety Commission. Though not shown, she is tasked with outcompeting and discrediting the existing club, which is assisted by 3 female students who function as her underlings.
After a calculated humiliation of the Newspaper Club's Yukari Sendou, and despite warnings from the club president, Kurumu coerces Tsukune to help her to distribute papers rather than burn them. At this point Keito ambushes them, informs them of the past club's punishment, and, while her minions restrain Kurumu, strings up Tsukune and reveals her true nature as a Jourugumo and as a student police officer. She also reveals that the 3 girls assisting her were members of previous clubs that the Public Safety Commission attacked and shut down, and that Keito had injected them with a kind of venom that made the girls, who were in fact semi-insect monsters, into her slaves.
She threatens to do the same to Kurumu, but the intervention of Yukari and Moka prevent this. In the resulting confrontation, Tsukune removes the Rosary, and is promptly rescued by Moka. After being taunted by the awakened Moka, Kurumu frees herself from Keito's web and the 3 enslaved insect monsters. Keito attempts to ensnare Moka in her web, but Moka effortlessly drags Keito towards her, who begins to become fearful and begs for Moka to stop.
Moka responds by throwing Keito into the air and kicking her away, with Kurumu following suit immediately. Keito is sent flying into her own web along with her minions, comically being wound up into a giant ball of silk, and bouncing along at high speed while her minions pledge their loyalty to her, much to her pain and chagrin. The large silk ball immediately strikes the ground with great force, leaving Keito's minions unconscious, and Keito herself just conscious enough to croak a compliant reply to Moka's taunt before passing out.
Her swift and decisive defeat leads to Kuyo and the rest of the Public Safety Commission to attempt to eliminate the Newspaper Club.