I'm not super familiar, but kimashitawa- roughly translates as "it's here" or "it's arrived"; the Pixipedia entry mentions that it's a very feminine way to say "kita-!" (standard 2ch exclamation). Recently it's become a minor (?) meme on 2ch which is used as an ascii art macro to express approval of a yuri pairing or situation, or to interpret an ambiguous situation in a yuri way.
The pun works something like this: "Kimashitawa-" (hiragana): the original line from Strawberry Panic. Apparently it was not yelled but rather whispered. "Kimashitawa-" (katakana): the ascii art, as well as the most common version of the meme. Part of the original joke probably comes from having this whispered line rendered as a yell. "Kimashi Tower": a punny misinterpretation of the katakana. This version has gained significant currency mainly due to its amusing non-sequitur nature.
My guess is that the ascii art, based on the original line, was what sparked off the meme. But I could be completely wrong on that.
Harime Nui Hououmaru ReiGood. Kiryuuin RagyoI wonder what the Tower of Kimashi is...How favorable.Tawaa!!!
This is a pun on some sort of meme/ASCII art that I'm not familiar with regarding the term キマシタワー (kimashitawaa) which sounds like Kimashi Tower if you separate it. The meme seems to have originated as a joke on how one of the girls in Strawberry Panic! spoke, adding a really feminine "wa" at the end of her sentences. Literally it translates to something like "It has come" and appears to be used (in meme form) when something yuri-like pops up.All that's left to achieve 100% shares for the Revocs Company is the completion of the Tower of Kimashi.End.KimashiThere's just a bit more until Shinra Kouketsu is all sewn up.What was the Tower of Kimashi again...