#034 of Atomic Bunko/Atomic Pocketnovels, the second volume of the story. Previous volume can be found: Vol.1
info on mugi: http://doujinshi.mugimugi.org/book/567294/
physical ver: http://www.amazon.co.jp/gp/product/4799200968/ (note this is one of the few with no bonus contents from physical version under this label)
digital ver: http://www.dlsite.com/books/work/=/product_id/BJ011039.html/