Akikan!

Kakeru Diachi collects rare juice cans as a hobby. After attempting to drink from one, he meets a girl he names Melon, due to her melon soda flavor. She is an Akikan, a type of attractive female figure designed to participate in a bizarre experiment comparing steel and aluminum containers. Kakeru becomes entangled in this unusual project, as Melon requires carbon dioxide to breathe, making her dependent on him. His childhood friend Najimi, who is wealthy and attractive, acquires her own aluminum Akikan, leading to further complications.