Yorinuki Gintama-san on Theater 2D - Shinsengumi Douran Hen (2012)

Demonic Vice-Commander of the Shinsengumi, Toushirou Hijikata, acquires a cursed sword--one which completely rewrites his personality, morphing him from a hard-boiled, no-nonsense cop into a hopeless otaku. As he struggles to break the curse, an ambitious new member of the police force, Itou Kamotarou, seizes the opportunity to depose Hijikata in his bid for power within the organization. However, Itou's scheme is revealed to be more devious than anyone imagined, and the very existence of the Shinsengumi is thrown into peril.