Rumi Shishido

The year is T.C. 4767. Four thousand years have passed since humanity abandoned its birthplace, the planet Earth. Beset by the hostile alien Gnosis, mankind is now scrambling to find ways to defeat this threat to their existence. The development of KOS-MOS (a specialized android with amazing capabilities) by Vector engineer Shion Uzuki was one response to the threat. But when their ship is destroyed by the Gnosis, Shion and her companions find themselves thrust into the middle of a battle with no clear sides...

It is the dark century and the people are suffering under the rule of the devil, Vandel, who is able to manipulate monsters. The Vandel Busters are a group of people who hunt these devils, and among them, the Zenon Squad is known to be the strongest busters on the continent. A young boy, Beet, dreams of joining the Zenon Squad. However, one day, as a result of Beet's fault, the Zenon squad was defeated by the devil, Beltose. The five dying busters sacrificed their life power into their five weapons, Saiga. After giving their weapons to Beet, they passed away. Years have passed since then and the young Vandel Buster, Beet, begins his adventure to carry out the Zenon Squad's will to put an end to the dark century.

Eight-year-old Doremi Harukaze aspires to be a user of magic, as she believes it would solve all her problems and help her confess to a boy she liked. One afternoon, she comes upon a magic shop and correctly suspects that the shop owner is a witch. The shop owner becomes a Witch Frog, "greenling", as this happens to witches when their true identities are discovered. In order to retain her original form, the shop owner, Majo Rika, takes Doremi as her apprentice to turn her into a witch. Doremi must take nine witch exams at night to become an official witch; however, she must never let her own identity as a witch be found out or the same fate that befell Majo Rika will happen to her.