The artist is ぱあこ(陸原一樹), but I can't romanize it.

According to his/her homepage it would be pako_(kugawara_kazuki) after we romanize it under our standards. I can't find that artist in danbooru database, though, neither can I find that picture in the gallery at the linked website.

E: ah, ok, I'm blind, there it is: http://www.leaffish.com/gallery/ill_o_digital/html/009_yukata2001.html

Type-kun said:

According to his/her homepage it would be pako_(kugawara_kazuki) after we romanize it under our standards.

ぱあこ would be romanized as "paako" under Danbooru standards.