Jun is a gifted little girl who fills her days building inventions, among them two small robots, Kichinosuke and Yukinojo, who become her closest friends. Her intellect gets her into college far earlier than usual, and there she falls for a classmate named Zero. Zero cares more about motorbikes than lessons and often skips class. Having fallen behind in his studies, he is much older than the other students and is ridiculed for it, while Jun is teased for being so young and small. A shared love of mechanics wins Zero's sympathy, and he agrees to have dinner with her at Harbor, the restaurant where her parents live. What follows is a comedy of lighthearted adventures and quarrels as Jun works to charm a boy twice her age.