On episode 21 (Another Zatch), Zatch remembers who erased his memories, Zeno, and tells it to Kiyo.Where Zatch really, really, really meets Zeno was in a sub:From Episode 147 (Reversed future. What episode in zatch bell does zatch meet zeno? He get angry at his father because Zatch obtained Bao without an effort at all and has a relaxing life while he has to go through painful training. Zeno later finds out about Zatch and Bao Zakerga being given to him. and finds that Zatch had a pretty harsh life in the momodo world: emotional and physical). yes, Zatch's memories were stolen by Zeno.

I should add that Zeno had to go through harsh training because he was known as the Momodo King's son and had high expectations while Zatch had a relaxing life in the countryside (later Zeno gives Zatch's memories back and. The father, of course, did not want Zeno to know about his younger brother because if he knew, he would chase after his brother and destroy his to obtain Bao himself. So the father sent Zatch Bell after giving him the Bao right after birth, hoping for him to control his power in the far future, to the countryside where nobody would know Zatch's true identity. Their father new that Zeno has a blood lust just like himself, and Bao could easily devour Zeno if he did not control it. It was a super powerful spell that helped the King get his throne. Bao Zakerga ate sorrowful and evil souls and thoughts.

So why did the Momodo King give Zatch such a powerful spell? The answer is because Bao is very dangerous. Zeno Bell hates Zatch Bell because his father (who was the King of the Momodo World during that time) gave Zatch the Bao Zakerga (or how ever you spell it) instead of Zeno, which is later revealed to be Zatch's older brother. I am not sure if the anime holds the same answer. SPOILER ALERT!!! SPOILER ALERT!!!All of this information is from the manga.

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