Maou Shoujo wa Pancake no Yume wo Miru

Otani Yorika (14) was a supporting character in his own life. After living such miserable days, Yorika committed suicide, only to find that an unexpected fate awaited him: becoming the demon king's pet in another world!? *"I'll defeat the demon king, gain my freedom, and finally become the protagonist of my own life!"* Yorika made this decision, and then a tiny demon girl appeared before him, with sturdy sheep's horns, moonlight-colored hair, and sparkling crimson eyes. (Source: Kadokawa, translated)