Hairu is a First Class Ghoul investigator and the partner of Koori Ui. She is the deputy leader of S1 Squad.

She is a veteran of the Owl Suppression Operation and serves as a member of Squad 0, commanded by Kishou Arima.

Ihei comes across as a normal young woman, though already a veteran Investigator. She eagerly and politely greets the Quinx, and is happy to finally have met people her own age. Though their superior, she wants to be treated as their peer and seems a bit uncomfortable with how young she is compared to everyone else she works with. She seems to have quite a tomboyish personality.

In battle however, Ihei is cold and ruthless. She maintains a casual personality in battle, even when fighting and killing ghouls. She has a habit killing her enemies brutally, and often leaves behind a gruesome trail of remains of her kills.

She later takes part in the ambush of Matsumae and her followers along with Taishi Fura, Shiki Kijima and Nimura Furuta. She dominantly fights against Matsumae with outstanding performance and she eventually wounds her belly. However, Matsumae has a chance to escape from her when Kijima captures Yuuma, one of her accomplices. Ihei is disappointed that Kijima obtained ownership Yuuma despite her great action.

She is later put in charge of the vanguard troops for the Tsukiyama Family Extermination Operation's second location, the Lunatic Eclipse Building. She easily fights her way in along with Kijima and the other CCG investigators and is confronted by Matsumae, Mairo, and several other Tsukiyama family ghouls near the top floor. After she witnesses Matsumae's kagune-formed sword and shield, Ihei expresses interest in getting it as her quinque. Despite the fight being more or less on even grounds, she slips on a pool of blood which created an opening for Matsumae to pierce Ihei with her kagune.

Though heavily wounded, Ihei demands her subordinates to hand over her other quinque. She fires T-Human at Matsumae, and begins to break through the her koukaku shield. Mairo leaped between the two women and took the fatal blow. He was torn in half, but still able to use the momentum of his leap to attack Ihei. Ihei had a vision of Arima and herself when they were younger and smiled before she was decapitated.