By day, Meimi is a typical orange-haired fourteen year old student at St. Paulia's Private School. At school, her strong point is physical education, but she's rather poor at math.

By night she transforms into the mysterious (yet magical) thief, Saint Tail. Saint Tail wears a long ponytail and is usually dressed in purple-black. In this guise, she takes back what bad people have stolen. She is given information by her classmate, and nun-in-training, Seira, of misdeeds.

Saint Tail is pursued by Meimi's classmate, Asuka Jr. An amateur detective, he's appointed by the mayor to catch the thief. By Asuka Jr.'s request, Saint Tail sends him notices of her crimes in advance, so he may have a fighting chance. As Saint Tail outwits Asuka Jr. in her capers, and as he chases after her with his eyes on only her, Saint Tail begins to fall in love with him. But as Meimi Haneoka, she always ends up arguing with Asuka Jr., for all he cares about is catching Saint Tail.

Unlike most other magical girls, Saint Tail does not have actual magic powers, instead she uses stage magic and theatrics to fool and confuse pursuers.