At just 14 years old, Theo Asper was an orphan and considered the weakest member of the mercenary guild. He was constantly dismissed by his peers and never allowed to join their quests. In his pursuit of strength, Theo learns about a ritual that can call forth a devil who can grant wishes. Desiring power, Theo successfully summons Helvi, an angelic woman. However, upon her arrival, he becomes enamored with her and wishes to marry her.
Despite opposition from both humans and monsters, Helvi is captivated by Theo's innocence and charm and accepts his proposal. With Helvi's unwavering strength, they surmount all obstacles and enjoy a fulfilling marriage.