Daichi Kakeru is a peaceful high school boy who likes to collect cans. One day, when drinking a melon soda, a girl suddenly kisses him. The steel can transformed into a girl who wants people to appreciate cans more. Kakeru names the aluminum-can-hating girl Melon and decides to take care of her, but every time he drinks from her melon soda can, which is necessary for her survival, they kiss.

As he learns to cohabitate with her, their fun-filled days are interrupted by a government agency responsible for the economy, who not only knows their secret, but introduces them to the Akikan (Empty Can) Elect, where steel and aluminum cans fight in order to decide who gets manufactured for the market. While Melon is eager to prove the supremacy of steel cans, her Owner, Kakeru, is strongly against participating, due to an incident in the past involving his rich childhood friend, Najimi, and guns that made him hate violence. However, there are other aluminum cans who are just as ready to battle as Melon and when those two natural enemies meet, it is kill or be killed . . .