Shhibaki is a high-school boy whose only interest is girls. Except he's been branded as the most perverted boy at school and the girls avoid him like the plague. One day he finds a book in the library about how to summon witches. He tries it as a joke, but it turns out to be the real thing. An apprentice witch named Rurumo appears to grant him a wish. Shibaki helps Rurumo and she in return refuses to take his soul. When the story starts, Shibaki wishes he could see Rurumo again. His wishes is granted immediately as Rurumo falls from the sky and crash lands in front of him. He finds out that as punishment for not taking his soul she's been busted down to an apprentice demon. Now, she must complete the task of getting Shibaki to use up 666 magic tickets that grant wishes before she can become a witch again. However, what she doesn't know is that each time he uses a ticket it shortens his life. When the last ticket is used up, Shibaki will die. Shibaki knows this because Rurumo's familiar black cat Chiro tell him as part of the "contract" for giving him the tickets. Now, Shibaki has a choice, make a wish and help Rurumo become a witch again or resist the temptation and try to save his own life.
As a member of the Mysterious Discovery Club, one day Shibaki Kota summons a witch using a witch summoning manual he found in the library. He asks for girls' panties. However, he had no idea. Having his wish granted meant creating a contract with a witch and giving her his life...
When Rurumo appears again, Kota receives magic tickets from her that allow him to freely use magic. Making a human use up the magic tickets was the demoted witch's training. However, Rurumo doesn't know the owner of the tickets dies once they're used up. When Kota learns this from Rurumo's Chiro, he swears never to use the tickets again.
Through the power of a memory alteration spell, Rurumo begins living with the Shibaki family under the guise of Kota's younger sister. Despite them living together, Kota experiences great distress at his inability to do anything to his "younger sister". Meanwhile, in order to punish herself for having too much fun, Rurumo begins working in the cafeteria at Kota's high school, where she makes mistake after mistake.
Strictly cracking down on students and beating offenders with their fists are the West High student council's student monitors. Student monitor Inoue Sumiko has known Kota since elementary school and cannot stand the sight of "Shibaki the pervert".
One summer Sunday, as Rurumo makes mistake after mistake while trying to clean the house, she is sent to deliver something to Kota, who is working at his grandmother's farm. Rurumo heads to the post office to purchase "stamps" to ride the train, with Kota's friends and acquaintances from school spotting her on the way.