Hakuoki Shinkai Reimeiroku

Years before the beginning of Hakuouki, the Shinsengumi was known as the Mibu Roushigumi. A wandering young man named Ibuki Ryuunosuke falls in with the group by chance just after they first come to Kyoto, and while grudgingly making friends with the members within, witnesses the dawning era of the Shinsengumi.