Eijirou Sharaku

Eijirou Sharaku (写楽影次郎, Sharaku Eijirou) is a martial arts teacher of Mairu and Kururi along side his younger sister, Mikage.

Characteristics
Eijirou is a seasoned martial arts instructor alongside his father and siblings. He is shown most often as having short brown hair, a short beard, and wearing a grey tank top and shorts. Eijirou is not described in detail in the novels and was first seen when character cards were released for the second season.

Adabashi Arc
Eijirou and his siblings are introduced. He is seen training Izaya's sisters and warns them about Adabashi.

Shingen attempts to bribe him to learn from him, but Mikage stops him.

He joins the chat room as Shoro.

Dragon Zombie Arc
Eijirou and Izaya fight outside the dojo until Mikage overhears them and puts a stop to it. Mikage 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 three block radius. Mikage lets Izaya escape and is about to leave when Eijirou stops her again. He asks if she is still interested in Izaya after all that he has done, and she knocks him out in response.

Izaya Orihara
Eijirou despises Izaya with a passion. His hatred for the broker comes from the fact that Izaya took advantage of his sister (who had a crush on him at the time, as Eijirou was aware of) when they were teens, and he manipulated her into the taking the fall for a scandal that made her drop out of high school, which forced her to take up the family business as she had no real options for work. This, as Eijirou claims, ruined her life. When he saw Izaya talking to the twins, he immediately attacked him.

Trivia

 * We can see a poster of him in Durarara!! x2 Ten Episode 4 at Russia Sushi.