One year after humanity was wiped out by an unknown virus that suddenly spread, three high school girls, Koharu Harumi, Natsuki Tsukishima, and Chiaki Akechi, spend their time using their school as a base and having fun that they were unable to do before. Nakakoharu finds a butterfly with a plant growing out of the bud of her flower. She even started to grow plants on various creatures such as dogs and cats... What exactly happened on Earth after the virus spread? ?