Satoshi Tainaka (田井中(たいなか) 聡(さとし) Satoshi Tainaka) is Ritsu Tainaka's younger brother. He first appears in Winter Days! when Ritsu is walking home with him from a movie they saw together. He then ventures off with a friend from school to their friend Suzuki's house. He later appeared once in a while during the series, for example when he brought his sister her student handbook in Plan!.