Yamato Keisuke, a promising freestyle swimmer, and Ninomiya Ami, a talented diver, are the offspring of two rival families owners of confectionery shops. Two generations ago, Grandfather Ninomiya came up with an idea for an owl-shaped cake, but Grandfather Yamato quickly raised to the challenge and thought of a similar cake—but in Yamato's the owl had ears. Because they're priced the same, Yamato's extra ears were crucial, and that made the business of the Ninomiya confectionery suffered. Grandfather Ninomiya then fell ill worrying about his shop. Before his death, his last words were "I was killed by the Yamatos," and since that moment the two families have been sworn rivals.