Imu is a third-year student at Hebijo Clandestine Girls' Academy and Miyabi's closest friend. Their deep bond began in childhood, forged through games of shinobi. One pivotal night, they stole their fathers' weapons and entered the forest, encountering a Yōma. Miyabi's mother intervened to save them and was killed, leading both girls to swear vengeance against all Yōmas. Imu later spent a year hospitalized after a mission where she and Miyabi ambushed a shinobi team hunting a Yōma; the creature exploited the chaos to kill most combatants. Imu witnessed Miyabi defeat the Yōma before collapsing into a coma. She remained steadfastly at Miyabi's side throughout the coma and subsequent recovery, which involved memory loss.

Following these events, Imu retired from active shinobi duty to dedicate herself to Miyabi's rehabilitation. She later collaborated on reconstructing the Hebijo Academy facility. Her protectiveness towards Miyabi is intense, including acting as a human shield. Imu possesses a somewhat naïve and otaku-oriented personality, frequently expressing anime-inspired sentiments. Her determination to destroy Yōmas equals or exceeds Miyabi's, and she voices frustration when their team lacks motivation during events like the Shinobi Bon Dance in Estival Versus.

Imu persistently tries to coax her younger sister Murasaki out of her room, though Murasaki often resists. Despite their differences and Murasaki's preference for solitude, Imu cares for her deeply. At Hebijo, Imu endured persistent harassment from Hikage, including incidents like her glasses being defaced with permanent marker, her washcloth swapped with deep-fried tofu, and her computer mouse replaced with a live mouse. These fueled Imu's desire for revenge, leading to confrontations where she declared specific grievances such as the "Battle of the Boxer Shorts" (referencing an embarrassing underwear exposure) or the "Skirmish of Sunglasses."

In combat, Imu wields a bo staff capable of altering its length and thickness. She employs shock effects to paralyze opponents and excels in fast-paced, close-quarters combat, particularly one-on-one. Her ninja arts feature wide area-of-effect capabilities effective against groups. During the Festival Eve Full of Swimsuits OVA, Imu arrives at a spa resort with the Hebijo group. She participates in the water cavalry battle after a truce breaks down and is present during the confrontation against Kuroku enemies summoned by Sayuri. Imu appears in other series entries: Shinovi Versus focuses on her revenge quest against Hikage, she is present in the Peach Beach Splash prologue when the team receives invitations, and in Bon Appétit! she attempts to engage Murasaki before leaving in frustration.