Himeno is a Public Safety Devil Hunter who serves as a supporting character. She is first introduced as the senior partner of Aki Hayakawa and a member of Makima's special squad. Her experience is evident in her demeanor and her history; she had gone through five different partners before being paired with Aki, all of whom died during their service. This traumatic past significantly shapes her worldview and her behavior throughout the story.

On the surface, Himeno presents herself as a carefree, light-hearted, and mature senior to newer recruits like Denji, Power, and Kobeni. She often uses teasing and jokes to motivate her subordinates, such as when she promises Denji a French kiss as a reward for defeating a devil. However, this cheerful exterior masks a deep-seated pessimism and trauma resulting from the repeated loss of her partners. She has developed a fatalistic view that devil hunters do not live long lives, a belief that leads her to adopt unhealthy coping mechanisms like heavy smoking and drinking. She even pressures Aki into smoking, arguing that they will not live long enough to suffer the health consequences. While she is generally kind and patient, she also has a stern and efficient side, especially when protecting her team. She does not hesitate to subdue panicked allies like Kobeni to prevent them from endangering the group. Deep down, Himeno is a caring and empathetic person who regularly visits the graves of her former partners, and her primary motivation is to protect her current partner, Aki, from sharing their fate.

As a devil hunter, Himeno has formed a contract with the Ghost Devil. This contract requires a significant sacrifice; she traded her right eye for the ability to summon and control the devil's right arm. This arm is invisible and intangible, making it a powerful tool for restraining enemies or striking them without warning. Despite this ability, she relies primarily on teamwork and strategy rather than overwhelming force.

Her role in the story is closely tied to Aki Hayakawa. She acts as his mentor, ally, and protector, and her feelings for him grow into a deep, romantic attachment over time. This attachment becomes her central motivation. When their squad is trapped by the Eternity Devil, she is willing to sacrifice the newcomer Denji if it means preventing Aki from using his cursed sword, which would shorten his life. Her fear of losing Aki is the driving force behind her actions.

Himeno's character arc concludes tragically during the Katana Man arc. After a surprise attack leaves her and her allies severely wounded, Aki is nearly killed by the Katana Man. Desperate to save him and with the Ghost Devil refusing to fight, Himeno makes a drastic new contract. She offers her entire body to the Ghost Devil in exchange for the ability to manifest its full, immense power. She successfully summons the devil, turning the tide of the battle and allowing Denji to recover and continue fighting. However, the Ghost Devil is then devoured by an opponent's Snake Devil, and Himeno's body vanishes entirely, leaving only her clothes behind. In a subsequent battle, Aki faces the Ghost Devil again, and a manifestation of Himeno's right arm reaches out to him, holding a cigarette with a message that gives him the resolve to fight without fear. Her sacrifice leaves a lasting impact on Aki, reinforcing the brutal reality of a devil hunter's life and the painful price of the contracts they make.