Kaze hikaru, volume 7 (Viz Media)

Akesato the courtesan has been instrumental in hiding the fact that Sei is a girl by pretending to be "his" lover. But Yamanami, another member of the Shinsengumi, has fallen madly in love with Akesato. As he struggles with the conflict between his comrade Sei and the love he feels for Akesato, he stumbles onto Sei's secret. Older teens.