He is the messenger and aid of Shinsengumi, a very diligent character that he was able to compile treatments for his comrades' illness or injuries.

The protagonist, Yukimura Chizuru, is the daughter of a doctor who works in Edo. The father leaves Edo to work as a volunteer doctor and moves to Kyoto without his daughter. As time passes by, Chizuru starts worrying about losing contact with her father, so she decides to go to Kyoto in search of him. On the way, Chizuru is attacked by few criminals and witnesses a fight between an oni and the Shinsengumi. Taking her into custody and saving her, the Shinsengumi debate on what to do with Chizuru when they discover that she is the daughter of the doctor they are also looking for. So they decide to become Chizuru's protectors and help her look for her father (the doctor). Lots of events happen while she stays with the Shinsengumi, as they discover mysterious secrets and also fight against the Bakumatsu group. The story is overall romantic with a historical and political background. 
(Source: Hakuouki official website)

The year is 1863 and as Japan's long festering wounds of political discord erupt into violent waves of street clashes and murder, the Tokugawa Shogunate sends a new force of masterless samurai called the Roshigumi to the aid of the Aizu forces in Kyoto. However the new "police" are anything but a cohesive force and assassination has already split them into two opposing factions. The stronger is led by the brutal Serizawa Kamo and the lesser by the more honorable but less assertive Isami Kondo. It is into this pack of wolves that Ryunosuke Ibuki is dragged by the rabid Serizawa. Forced to be a virtual slave by blood debt, he hates the samurai and everything they stand for. But as he sees how the other half of the samurai live, he begins to believe that there may still be a chance, for both himself and Japan, if only Kondo will step up and take down the mad dog Serizawa! 
(Source: Sentai Filmworks)

This OVA takes place in between episodes 8 and 9 of the first season of Hakuouki. 
Yukimura Chizuru goes on a reconnaissance mission in Shimabara as a geiko for the Shinsengumi. Each episode unfolds the events of the days leading up to, during, and after the operation. It intermittently reveals each captain's involvement as well as that of a few demons in the affair. Each individual episode primarily focuses from the third person perspectives of: Okita Souji, Saito Hajime, Harada Sanosuke, Toudou Heisuke, Hijikata Toshizo, and Kazama Chikage.

Based originally on the famous otome game, this series is Ninomiya Sachi's version of Yukimura Chizuru's story as she arrives in Kyo from Edo to search for her missing father and accidentally meets the members of the Shinsengumi, who harbor an awful secret.  Unique from other versions, this series unfolds a bit out of order, starting already at the Ikedaya-jiken and then progressing with flashbacks.

Based originally on the famous otome game, this series is Hiraku Naki's version of Yukimura Chizuru's story as she arrives in Kyo from Edo to search for her missing father and eventually becomes involved with the Shinsengumi.  This version begins the night that she meets the members for the first time.  

A novel adaptation of the game "Hakuoki", following Hajime Saitou's route.

A collection of short stories, each split into two parts, all based on the famous otome game and anime series, Hakuouki, which follows Yukimura Chizuru as she begins her journey to find her missing father in Kyo and meets members of the Shinsengumi, who harbor an awful secret. 
 
Each story is written by different authors and is meant to individually highlight Chizuru's relationship with one of the main characters of the series. Consequently, there is a story dedicated to Hijikata, Okita, Saitou, Harada, and Heisuke.

Members of shinsengumi are students or teachers.

Susumu Yamazaki