On a picnic at the beach with Suzy, Kiyo and Zatch are practicing the fourth spell when suddenly they hear someone singing a song in the distance. Approaching the voice, they find a little boy named Yopopo in a green outfit dancing to the song. When Zatch playfully starts imitating the dance, a girl named Djem appears. Though at first she assumes that Zatch is a mamodo and attacks him, seeing Kiyo makes her think she is mistaken, and she invites Kiyo and Zatch for lunch. As Djem begins spilling the story of the Battle of 100 Mamodos, she explains that her mamodo, Yopopo, with whom her relationship has soured, has the power to attract other mamodos with his song and dance. Meanwhile, Suzy notices that Yopopo has disappeared. Only Djem knows what it means; Yopopo has found a mamodo and has gone to fight alone... without his book of spells! Djem is furious but Kiyo and Zatch see that Yopopo wants to protect Djem...for it turns out that he is fighting the cold-hearted giant mamodo ...