I almost forgot about it until GoddessofFailure mentioned it.

I just realized something. In Hidden Star, Cirno represents summer.

Autumn (in 2017) starts on September 22.

GASP CIRNO DAY IS IN THE SUMMER HOLY SHI-

Wow, what a coincidence here.

Just a buncha more years left until the next Perfect Cirno day. By then, we would be dead.