So, here's the first Kyoukai no RIN-NE group ever at Sakura Con! I'm fairly certain of it. We might be the first group at a Pacific Northwest con...not sure. I'm sure there'll be more, especially once the series has an anime.
Lady Shinsei did the bakeneko illustration of Rokumon herself...really fantastic! She nudged me into pulling together Sakura for the con, since I didn't want her to be the only RIN-NE cosplayer there.
If you're interested in the series, go to http://www.shonensunday.com/series/rinne and scroll down to the manga viewer. Viz does simultaneous English translations of the Japanese version in Shonen Sunday each Wednesday. The first 2 volumes are out in print.