The anime is set in the birthplace of the popular card game Rush Duel, Mutsuba-cho. Twins Yūhi and Yuamu run UTS (Uchūjin Trouble Sōdansho or Alien Trouble Consulting), a group that (supposedly) gets rid of troublesome aliens from distant sectors of the galaxy via Rush Duel battles. However, one day, they find an actual spaceship, and inside they find Yudias, an alien from the Belgar Cluster. Yudias has come to Earth to search for Rush Duel to hopefully lead him and his friends (who have been chased out of their star system) into a new future. However, Yudias himself knows nothing about Rush Duel. Yūhi then challenges Yudias to a duel.

Hitoyoshi, a high school kid who lives alone, hears a knock on his door. He opens it to find a strange girl offering to be his maid. She has beautiful black hair, graceful manners, and…a dark past as an assassin. But despite her deadly background and lack of household skills, Hitoyoshi takes her in. As she adjusts to her new life, she begins to experience emotions she’s never felt before.

Zenitendo is a mysterious candy store that only lucky people can reach. All the candy recommended by Beniko, the owner of the store, is perfectly suited to the buyer's troubles. However, it depends on whether the candy will be used or eaten correctly that it can bring happiness or misfortune.