Agerna is a planet rich in Vizorium, the one mineral necessary to space travel. So when a series of mysterious attacks on mining operations has the governments of the world pointing fingers and blaming each other, the World Welfare & Works Association naturally sends in their top agents to investigate. But are the lovely angels up to the task of stopping a mad scientist bent on taking a long dormant alien race to its final evolutionary form? Throw in a thief who's hunting a bottle of World War II-vintage wine and it's a safe bet that nobody on the planet is safe. It's more chaos, more mayhem and even more destruction than ever before as the Dirty Pair take on their wildest case yet!

In order to take over her grandmother's Dagashi store, art student Kumi Honamanuma moved to Kyoto. She met Harami Mino, K Kusanagi, Mai Haisaka, and a dog who lives in the store, which supposed to be empty. Kumi ended up living with these girls, who claim that they are heroes reincarnated to contemporary period to chase after the demon king. Harami and others seem to live in a peaceful life with no missions to to do anymore, Ran, who was demon king in the past and appears to be an elementary school girl from failing to reincarnate, one day. The story begins with Ran requesting to collect demon king's fragments.