Maou Gakuen no Hangyakusha: Jinrui Hatsu no Maou Kouho, Kenzoku Shoujo to Ouza wo Mezashite Nariagaru

To demons, humans are nothing but slaves. Morioka Yuuto, an ordinary high school boy, is selected as a candidate to be the next demon king. He is admitted into Ginsei Academy, a school for demons where he's scorned upon by the other students.
"...I'll make you the demon king. So... make me your kin."
After meeting Himekami Rizeru, a beautiful demon girl, Yuuto's world begins to change.