Choukyou Injoku Hime Sylvia ~ Majuu Seidorei no Rakuin

Princess Sylvia's daily job as a ninja consisted of defeating monsters while wielding a giant sledge hammer. However this time when the Princess goes into the village to defeat the monsters which have appeared, she and her lady-in-waiting, Paratua, are caught in a trap by the demon Marz.

What waits in store for them is a repulsive and lecherous violation banquet held by the monster hordes themselves!

[From DLSite]