Extended Summary

When the Bell twins were born, King Bell sealed Bau Zakerga inside Zatch. When he was about to mention separating the two brothers so that Zeno could never harm Zatch for getting a power he didn't have, he remembered one of the two promises he made to his Book-Keeper, Princess Sakura, to never let his children grow up apart from each other, as they would be each other's greatest strength. The Book-Keeper also told him that his children would balance each other perfectly in all aspects, from physical strength to personality.

Keeping the promise, the twins grow up together in the palace. As the years passed, King Bell saw that his Book-Keeper's words were indeed true. While the twins made friends, rivals and enemies, they truly complimented and balanced each other perfectly.

When the twins were 2-years-old, they began training in how to use their powers, and at the age of 4, they went to school with the other mamodo children, Zeno to military school and Zatch to private school.

Unfortunately, the other promise he had made, he was unable to fulfil. He didn't know that his sons would be the ones to fulfil the promise their father made, without even knowing it.

Though because King Bell was unable to fulfil his second promise, the spirit of his Book-Keeper returned to Land of the Living, just before the start of the Battle to Determine King of the Mamodo World, to sleep within her reincarnation, Sakura Takamine. Sakura has experienced unimaginable pain and has forgotten how to smile. Unfortunately, because of the spirit sleeping within her, she is unwittingly drawn into the Battle.

Will Sakura remember her past life? Especially when Zofis awakens the Ancient Mamodos? And will she have the courage to open her heart to love, once again?