In a magical world where demons threaten humankind, the heroine Zeno rises up to be their champion! There's just one problem: the reigning Devil King is a baby, and she can't exactly slay a baby. Even if this domineering monster baby has crass tastes and evil DNA, she believes he can be turned to the side of good with the right influence. Unfortunately, she's forced to test the theory when a contract binds her to the baby Devil King as his surrogate parent until he performs enough good deeds to prove his worth. What kind of role is that for a mighty hero? Oh, mama!