Kaori Yumiko is a high school girl with large boobs and a track athlete. One day, she is hit by a car and seriously injured, but her life is saved by surgery performed by Dr. Osuga. However, Yumiko's breasts have been transformed into a peculiar condition where they become huge when she gets excited! Using the power of her gigantic breasts, she wins the track and field championship. She quickly becomes a beautiful busty idol star, but then another super busty idol appears who persistently harasses Yumiko. In fact, this idol is a member of the evil busty army "Ura Mespai"! And Dr. Osuga is none other than the head of the Japanese branch of "Mespai," a secret female organization fighting for world peace. Now the final battle between Ura Mespai and Mespai has begun!