Where is this from? Googling tsuyagaaru didn't help, as it only refers to a yaoi manga. Funnily enough, this image doesn't look like it's from a yaoi source...
It's a ren-ai game for girls, taking place in the days of the Shinsengumi. I think the girl is the protagonist. itunes calls the game yanga-ru.
Pixiv title of the image すんたまと混浴 (Suntama and mixed bathing).
