Celo, a priest of light, is forced into exile from the party of heroes after he protects the heroes from the Sixth Demon King's curse and turns into a demon tribe. He meets Lucy, the daughter of the Sixth Demon King, who sees his potential as a Demon King, and together with the demons under his command, he develops his territory. Then, a party of heroes arrives to defeat Celo. When they enter a tomato field under the castle, they find a demon enhanced by Celo's skills lurking there...?