The date is a pun:
Iku → i(1) ku(9)(A sarcastic cheer for dragoons' pitiful performance at the time)Iku
They say the cry of "Kyaa Iku-saan" that sounds like something one would say to an old acquaintance is originally based on the "Kyaa Ryuu-san" self-deprecating joke related to dragoons in FFXI!
Dragoon is said in Japanese as ryuukishi (lit. dragon knight). Ryuu-san would mean Dragon-san.
Kyaa Iku-saanhas also become widespread in the Japanese touhou fandom.Well I can't really say I dislike itBut showering me with those shrill cheers is not going to get you anywhere.Kyaa Iku-saan!Myonhold