Akikan!

Akikan ("Empty Can") is the unlikely story of high school boy Kakeru Daichi, whose can of melon juice soda magically transforms into a human girl. More "akikan" girls begin appearing, each of them needing to be infused with carbon dioxide from their respective drink types to survive. The akikans were created as part of the 'Akikan Elect' to determine whether steel cans or aluminium cans are superior. The akikans must battle each other until only the strongest can type is left standing. Source: Wikipedia