Asuka Kouzuki is just a normal twelve-year-old girl on spring break -- until she learns she's from a long line of phantom thieves! For generations, her family has been stealing from bad guys and helping others, and her dad has been secretly teaching her the skills for the job her whole life. Now that she's about to turn thirteen, it's time for her to take on the role alongside her cousin Kei, a genius with an IQ of 200. Thanks to her superhuman athletic abilities and his smarts, no ill-gotten treasure is safe at least, if they can get along.