18+ Maou na Ore to Ghoul no Yubiwa

Kusumi Chiharu gets a message one day that he has been selected as a Monster Tamer, and he is prompted to select his first partner. He thinks little of the message until he receives a giant package the following day. He assumes it's the porn books he ordered, but the huge box ends up containing the unconscious body of a mostly naked girl! She's a ghoul named Zonmi, who intends to fight with him as his partner. However, it turns out that other hot girls at his mostly-male high school are also magical creatures, and Zonmi may not be the only one who wants to fight by his side!

(Source: MangaHelpers)