A little background on this picture: March 8th is Escalator Day in Japan. The 7th of every month is Rumia Day, because of her phrase "Sou nano ka?" (nanoka means the 7th of a month). The 9th of every month is Cirno Day, for obvious reasons. The 8th of every month is Daiyousei Day, because she falls in between Rumia and Cirno as bosses in Embodiment of the Scarlet Devil.

Thanks for the background info, now I have three more days to celebrate each month!