DHA sono roku!

is the sixth volume of the DHA light novel series, written by Rin Yuuki and Illustrated by Yuta Komiya. It was released under the Dengeki Bunko Imprint in October 2006.

Synopsis
Hello. This is Ai Shiratori. I ... I still can't believe it. --Mitsu-kun is the greatest person of the devil ... Lucifer. The devil girls made "the seven deadly sins" commit and "corrupted" Mitsu-kun ... Only I, the only one in the world, can save him. The only way to save him from "corruption". It's about "contracting" with me! I said! It's a shame !! No matter how much you like it, it's a good idea to order things! Well, first we get to know each other, then ... we don't have that much time anymore. I have to help Mitsu-kun as soon as possible ...!

(source: Bookwalker JP - Translated)