Ding Dong! I opened the door and saw a little boy standing at the door. He handed me a box of exquisite tissues as a greeting gift and said, "I am Sato, who just moved to Room 203. Please take care of me." This is Sato Kotaro, a four-year-old who moved to Shimizu Apartment to live alone. He put a toy sword on his waist and went on his daily shopping trip. Mature and naive, Kotaro infects the people around him with his smart way. This is a story about a four-year-old boy who decided to be strong until the day he can live with his parents.