30-year-old Kenji lives alone in an old house, which is set to be demolished for redevelopment. His mother has been missing for years, his father runs an inn in a rural area and his younger sister travels all around the world. Kenji has been left all alone. He holds a job that doesn't have a future and his life is boring. The time approaches that Kenji must evacuate from his home. Late at night, Kenji's boss skips town and he loses his job. He has nothing to do and nowhere to go. Kenji gives his house key to a real estate company and continues to stay there. Suddenly, three young children named Korosuke, Yataro and Occhi appear and begin to attack Kenji's house with water balloons. Kenji counterattacks by spraying them with a water hose. Since that time, the 3 kids visit Kenji every day and play with him. Kenji makes a promise to Korosuke, who doesn't have a mother, to take him to the aquarium one day. Nozomi graduated from the same school with Kenji and now works for a real estate company. She visits Kenji's home and asks him whether he has a reason that he is still staying there. Kenji can't provide an answer. That night, Korosuke comes alone to visit Kenji, but Kenji kicks him out.