Negai wo Kanaete Moraou to Akuma wo Shoukan shita kedo, Kawaikatta node Kekkon shimashita: Akuma no Niizuma  

I Summoned The Devil To Grant Me a Wish, But I Married Her Instead Since She Was Adorable ~My New Devil Wife~, 願いを叶えてもらおうと悪魔を召喚したけど、可愛かったので結婚しました　～悪魔の新妻～

14-year-old orphan Theo Asper is viewed as weakest member of mercenary guild due to his constant dismissal from parties he joins. In search for strength, he discovers ritual that summons wish-granting devil. Despite naively intending to ask for power, Theo's only wish becomes marrying an angelic woman named Helvi when he sees her before him. Charmed by his cuteness and innocence, Helvi agrees to marry him. Although many people and monsters try to disrupt their relationship, Helvi's overwhelming strength easily overcomes any obstacles, leading them to a happy newlywed life.