Spring Fling is a story written by Shinko Hisada and illustrated by Ravyn. It ran in Issue 15 at http://s2b2.livejournal.com/86741.html, and is mirrored at http://www.shousetsubangbang.com/mirror/spring-fling/.
From delicious.com: "part of a series, but stands alone. it's May Day and the festival is spewing magic about"
This story is part of a larger arc, the complete order of which can be found here.