Iroha Mayuzumi (黛彩葉, Mayuzumi Iroha) is a character in the Izaya-centric novels and a driver for Yuuki Usubara.
Iroha is described as a slender yet muscular woman, having short hair with one part of her bangs covering one eye.
While she was an assassin, she briefly mentioned that she felt she was unfit for it due to how soft and compassionate she had grown for others. This change is most evident when Iroha is shown as being sympathetic especially towards children, worrying to herself a few times over Haruto and how she doesn't want to see him cry if something happens to Izaya, despite being a trained killer for years.
Iroha was abandoned by her family at a young age only to be taken in by an organization and raised to become a killer. This organization instilled her with various skills, techniques, and readiness, to perform the murders they wished for her to carry out. A majority of Iroha's targets were people of underground organizations who opposed her foster father, in order to survive, Iroha was required to kill. At the age of fifteen, she was sold by her adoptive father to Ryuusei Takioka.
The name "Iroha Mayuzumi" is not her actual name but an alias purchased off another person via Kasane Kujiragi. Following Ryuusei's purchase of her, Iroha's life-long training 'to blend in with the general public' was put to the test. She was able to adapt herself well enough to blend in with society and be thought of as a one of them, working as a beer server out in the stadium publicly while actually hired to dispose of bodies under the Third Investigation Team by Ryuusei.
When first introduced, Iroha is out selling beer near the unreserved seats of the Natsugawara's Stadium while keeping watch of Izaya under Fudou's orders. When she intends to approach him, she and Haruto accidentally collide while the boy just bought an ice cream, and having a soft spot for children, Iroha buys him another one. When she watches him return to the a man in a wheelchair and the old man behind him (Sozoro), she immediately notices he's a dangerous man she could not win against. Afraid to approach, she instead keeps watch from a distance for the time being.
Receiving a direct order from Ryuusei, Iroha heads to the VIP room where Izaya Orihara and the vice governor Hiura are. She changes into bartender's clothes as a disguise to get near him. This surprises Izaya while he is conversing with Hiura, and she sees it as an opportunity to slice his throat. However, she withdraws with Sozoro behind him and leaves the scene to accomplish another task.
She is told to look after the hostages, Haruto, Himari and Yuuki Usubara. She behaves in a polite manner with them, fearing the next order would be to kill one of the kids, even though the hostages already suspect what Iroha's job really is. Yuuki offers herself to accompany her when Iroha is ordered to bring a hostage to Ryuusei's office, knowing it would be better for her to go than the kids. Just as they arrive, Yuuki is knocked unconscious by Fudou and Iroha tries to attend to her as Usubara, witnessing the scene, goes berserk. After she makes sure Yuuki is safe, she begins to fight with Usubara rather than Izaya so he does not get killed.
When Yuuki recovers, she manages to stop the fight between the two and offers Iroha a part time job as a driver to continue looking for Izaya.
- It is stated that her adoptive father was killed in a fight a few years back in Kyushu. Iroha could not fully recall the name other than the person responsible was some sort of samurai hitman. This is a reference to the Niwaka Samurai, a famous killer and urban legend in Fukuoka in the series Hakata Tonkotsu Ramens.