Cho Sang-gu is an ex-convict and Geu-ru's estranged uncle who becomes his guardian upon release from jail. He is blunt, smokes cigarettes, and moonlights as an underground MMA fighter. He was sent to jail after putting his protégé Su-cheol into a coma during a fight. Despite his background, he is still entrusted to take care of Geu-ru after his release, and is instructed to stay and work with Geu-ru for a three-month probationary period.
Although he initially does so for financial gain, and appears to be ignorant of Geu-ru's condition, he slowly gets to know Geu-ru as they both work together as trauma cleaners for Move to Heaven, gaining a new outlook on life and allowing him to discover the truth about his half-brother and Geu-ru's father Jeong-woo, whom he mistakenly thought had abandoned him when he was still very young.
