Negai wo Kanaete Moraou to Akuma wo Shoukan Shita kedo, Kawaikatta node Kekkon Shimashita: Akuma no Niizuma

Theo Asper is a member of the mercenary guild, who has already joined and been expelled from several adventurer parties. The reason is simple, he is too weak. Wanting to become stronger, Theo summons a demon to make his wish come true. But the moment he laid eyes on the demon he summoned… the dreams...

Source: MyAnimeList