Ai Morikawa is a hard-working career woman at her job in Tokyo. After a long night at work, she returned home on the last train to find a handsome boy at her door. The 16-year old Nagisa is her sister's stepson, suddenly sent to live with Ai when his parents left for an overseas job. Wary like cats, these two loners 10 years apart in age will have to make a new life together.