Empty Can! 

The story revolves around a typical high school boy named Kakeru Daichi and the can of melon juice soda that he bought from a vending machine. The can suddenly transforms into a beautiful but standoffish girl that Kakeru nicknames "Melon," and more "Akikan" ("empty can") girls appear. However, Akikan girls need to be infused with carbon dioxide in order to turn into a human.