Naota is just a normal Japanese 6th-grade boy (although just a little cynical), but when his older brother leaves for America to play baseball, his brother leaves his 17 year-old girlfriend Mamimi behind. Mamimi is sending mixed signs and improvements into Naota, also he does not know what to do about her. But to make matters even worse, the world of Naota is turned upside down when a woman on the Vespa runs him. In their initial encounter, she hits him across the head with her guitar, and this causes a horn to grow out of his forehead. She calls herself"Haruko" and her existence changes Naota's life to further insanity