Daichi arrives on the Moon and hears the strange stories about people with rabbit ears. Soon he meets V-Mei, an old witch and her granddaughter Guri Guri, the members of the Long-Ears race which is in war with the evil Jadou Clan who wants to conquer the world. Sensing a power in the boy, V-Mei gives the magic gun to Daichi and reveals to him that he is the chosen Madou Warrior who will save the Long-Ears race and their land Rabiluna from the evil Jadou Clan. With the magic gun, Daichi can summon Granzort – the Madou King of Earth – a giant robot to fight against the monsters of the Jadou Clan.

(from Wikipedia)