Doc is the elderly proprietor of the Hanazono clinic, a medical practice located in the heart of Shinjuku. Despite the clinic’s modest appearance, it serves a very specific clientele, as Doc is known for looking after the numerous denizens of the underworld who inhabit the district’s shadows. This vocation is not a lucrative one; his commitment to treating those who cannot go to regular hospitals means he often struggles to make ends meet. To supplement his income, he occasionally takes on a second job working as a barker at a club. Despite these financial hardships, his skill as a physician is never in question. He is a highly capable doctor whose abilities are respected by those who know his true nature.

Doc has a long and significant personal history with the series’ protagonist, Ryo Saeba. This connection predates the peaceful but melancholic days of Angel Heart, reaching far back into the violent period of Ryo’s childhood. In his younger years, Doc served as the medic for a guerrilla group that the young Ryo belonged to while living as a mercenary. In that capacity, he played a crucial role in saving Ryo’s life, treating him for the effects of a dangerous drug known as Angel Dust, which had been administered by Ryo’s adoptive father. This shared history establishes Doc as one of the few individuals who is intimately familiar with Ryo’s dark past and has earned him a unique, trusted position in the sweeper’s life. Because of their long association, he acts as a confidant and a pillar of support, often filling the role of a paternal figure for the otherwise solitary Ryo. Furthermore, the connection between Doc and Ryo extends to the clinic itself; it is implied that Doc had previously employed Kaori Makimura as a nurse when she was approximately the same age as Xiang-Ying, the girl who would later receive Kaori’s heart.

Doc plays a pivotal role as one of the first people to recognize the miraculous return of Kaori’s spirit. He is acutely perceptive and is noted to be the second person, after the ex-soldier Umibozu, to realize that Kaori’s essence lives on within the young assassin Xiang-Ying. This realization occurs after a chance encounter in a dark alley, where a desperate Xiang-Ying was searching for the meaning behind the XYZ symbol associated with Ryo. When Ryo later brings the injured girl to his clinic, Doc is able to perceive the truth; he understands that Glass Heart is the recipient of Kaori’s transplanted heart and that she carries Kaori’s memories and emotions within her. This awareness allows him to transition from simply being Ryo’s old war medic to becoming a key supporter of this newly formed, unconventional family. His clinic serves as a neutral ground and a refuge, a place where characters like Ryo, Umibozu, and Xiang-Ying can seek medical aid and, just as importantly, find understanding and counsel. In this way, he helps bind the broken threads of the characters’ pasts to their hopeful future.