Susumu Makino (牧野 進,Makino Susumu) was the son of Chieko and Haruo, and the younger brother of Tsukushi. He was a middle school during the time Tsukushi was attending Eitoku Academy.
Susumu was born into a humble, middle-class family. He was the only son of Chieko and Haruo, and younger brother of Tsukushi.
His sister began attending the elite Eitoku Academy, while Susumu began going to a normal middle school. A year later, he became concerned about his sister, who had started acting strange during the mornings. He stated that "the stress is gonna make her snap." Tsukushi continued acting strangely at mealtimes. Several days later, the Makinos were visited by Tsukasa Domyoji, who stopped by to see a sick Tsukushi. Their parents fawned over him after learning he was the heir to Domyoji Group.