Driven by guilty for being incapacitated by tuberculosis, Okita Souji drank the elixir and became a Rasetsu in order to continue with his duties as the Captain of the First Division. Unfortunately, despite having accelerated healing, it does not completely cure his illness. It does, however, allow him to live out his final days somewhat normally, even if it would seem to be arguably shorter.
I’m sorry, but after I finished Souji’s route in the game, I felt really terrible. Then again, I don’t think any of the routes in Hakuoki ~Shinsengumi Kitan~ ended happily knowing some of your comrades died in the war. Anyway, thanks to Jenny for sending this in!