Mikage Sharaku

Mikage Sharaku is the martial arts teacher for Mairu and Kururi. She has two older brothers whose names are Eijirou (second oldest) and Eiichirou (oldest). She and her siblings teach at Rakuei Gym and are introduced in volume 08 of the Light Novels.

Characteristics
Although she doesn't look it at first glance, Mikage has incredible physical strength (enough to damage concrete) and reflexes. She has short brown hair and (as Eijirou frequently points out) a flat chest, though this doesn't seem to be the case as she is shown to have a developed bust, as shown when Izumii threatens her and messes with her shirt, we see that she has breasts. She is capable enough to take down several armed men at once but has a tendency to go overboard (especially where her brother Eijriou is concerned).

Mikage is also described as being tomboyish by others which was likely developed over the years of training she's had. She's usually level headed but can get easily flustered when her inexperience with romance is brought up. As seen in volume 09, she also has a strict sense of morals. When Izumii incapacitates Earthworm and is about to rape her, Mikage steps in and forces him to stop, saying that she would've been fine if he was just going to kill her quickly but if he truly intended to violate her then she would have no choice but to kill Izumii herself.

Adabashi Arc
Mikage as well as her siblings are introduced in this volume. They don't appear to play any siginificant role until near the end. Mikage gets an invitation to Izaya's office and she agrees to go. While she walks, she encounters Izumii Ran and the two appear to know each other rather well. When they arrive at the apartment they also see Adabashi Kisuke, Haruna Niekawa, and Slon already waiting for them. Izaya and Namie also enter with Izaya explaining that they are all his friends and invites them to have a hotpot party with him.

Dragon Zombie Arc
Mikage overhears her brother and Izaya fighting outside her dojo and decides to put a stop to it. She berates and severely beats Eijirou for disgracing the name of their gym by starting a fight in public (as well as proclaiming she was raped to everyone within a threeblock radius). She lets Izaya escape and proceeds to leave before Eijirou stops her again. He asks if she was still interested in Izaya after all that he's done and she simply knocks him out in response.

Mikage appears again along with Izumii, Haruna, and a small group of members of a gang called Dragon Zombie in order to rescue Izaya who had been kidnapped by two groups called "Heaven's Slave" and "Amphisbaena." After Izumii tricks them into releasing Izaya, Mikage and the dragon Zombie members bust in to incapacitate the henchmen (although it was Mikage who did all the actual work). When Izumii incapacitates Earthworm and is about to rape her, Mikage intervenes and threatens to kill Izumii if he goes through with it. Although he leaves Earthworm alone, Izumii threatens to do the same to Mikage. She brushes him off and dares him to try it if he was that confident. Seeing that she was serious, Izumii backs off and leaves. After the operation draws to a close, Mikage simply returns home.

Saving Izaya/ Haruna is back Arc
Mikage, Kine, as well as a few members of dragon zombie catch Slon (who at this point is being controlled by Kujiraki) attempting to carry an unconcious Izaya out of his office. After incapacitating the Dragon Zombie members, Slon attempts to throw Izaya at Mikage in an attempt to catch her off guard however she simply kicks Izaya out of the air. Kine and Mikage eventually overwhelm Slon and force him to retreat through a window. As they go  to check on Izaya's wounds, they find out that he has been awake the entire fight and simply pretended to be knocked out.