Semi is a cicada insect, born under a garden by an apartment building. After living underground for a long time, he finally emerges to the surface. At this time, Semi senses a woman is about to fall on him and he is able to avoid her. The woman is Yuka, who lives in the nearby apartment building. She works at a food company and appears to be lonely. Semi wants to make her smile. He changes his appearance into a human and he tells Yuka "Let's live together for 7 days." Semi tries to make Yuka happy for those 7 days and she falls in love with him, but he has that much time to live.