#043 of Atomic Bunko/Atomic Pocketnovels. The title suggests this to be a funny one (as this label supposed to be), good reading for those who fond of role-playing style story.
info on mugi: http://doujinshi.mugimugi.org/book/563053/
digital ver: http://www.dlsite.com/books/work/=/product_id/BJ015413.html
Honestly, I think it's about time we should consider a new category for hentai novel. If you search "novel" tag, there are about 900 galleries already and it keep growing.