Based on a popular otome game, Hakuouki follows Chizuru and the Shinsengumi in an alternate reality. Chizuru travels to Kyoto in search of her missing father but after being involved in an incident, ended up being taken in by the Shinsengumi where she meets the members including the famous Hijikata Toshizo and Okita Soshi. Chizuru’s father was conducting government research for strengthening the Shinsengumi and developed the ochimizu. The ochimizu is a formula that gives demon like strength and regeneration effects but once taken, the user experiences extreme pain and eventually turns into a blood hungry monster.
In an attempt to defend Chizuru, Hijikata takes the ochimizu and although the situation was saved, he is now affected with the illness. Okita is also forced to take the formula when his tuberculosis prevents him from defending Chizuru and himself. Feeling responsible for their actions, Chizuru must fight her feeling of helplessness and find the courage to support the Shinsengumi.