Muumu is an orphan mamodo, that had a sister that is dead, who left a doll. Muumu always leaves food for this doll imagining it to be his dead sister. His sister always said to him that if he asked for food while facing toward the king Mamodo, he will bring food, but his sister became sick and died. Because of that, he believed that the king wasn't a good person. A day later, the King appears to play with him, but he doesn't know that Zatch is the king. Later, Jiiza tells him that Zatch is the King, and paid Muumu to steal the mace that Zatch has, which has demonic power negating effects. He steals the mace and gives to Jiiza and Jiiza attacks Zatch with Bidyuron. Zatch tries to defend with Rashirudo, but the stolen mace negated his attack. After that, he takes back the money, kicks Muumu and stepped on Muumu's house. After that, Jiiza tried to kill Muumu using Bidyuosen and Zatch protects Muumu with his body. Jiiza using the chance to kill both of them uses his most powerful spell, Negurono Zoou Bidyun, and Zatch used Baou Zakeruga to defeat Jiiza. At the end, Zatch introduces Muuma to his classmates at his school.