Torture Princess: Fremd Torturchen, Vol. 4 (light novel) — Keishi Ayasato

I will put you down myself.
The Torture Princess has fulfilled her duty, and the fourteen demon contractors have been laid low. Yet, when the time comes for Elisabeth to burn-forsaken by heaven, earth, and all of humanity-the fifteenth demon contractor, Kaito Sena, host of the Kaiser, appears and declares himself the enemy of mankind. In light of this, Elisabeth receives a new lease on life as the heartrending task of hunting him down is forced upon her. Now on the run, Kaito and Hina find themselves in the company of beastfolk who wish to "receive the enemy of mankind as an honored guest." They are not without their own share of problems, however. Someone has been slaughtering their kin in the most gruesome ways imaginable. If Kaito's instincts are correct, these killings could be the work only of demons. But the demons have been dealt with...Haven't they?