Kiriko is a doctor who doesn't treat patients but instead, helping them to end their suffering lives (with permission).
Unlike his older self, Kiriko shares the same ideals as Kuroo Hazama; "to save the patient no matter the impossible." It is shown during Episode 5 of Young Black Jack, that he would go to great lengths to reach a patients, such as parachuting down a helicopter because the terrain was difficult. He is shown to be quite humorous, amicable, and very ambitious. Brave and willing to take risks (Episode 6), he stakes more on experience than hand-down knowledge, such as using anti-coagulant in amounts more than suggested (as opposed to what Kuroo inquired from book-knowledge) for a bullet-wound surgery.
He develops a more cynical viewpoint of things in general, tend to be more pessimistic to the medical conditions of his "patients," then resume to euthanasia, in such several patients that Black Jack managed to save, including his father (despite further complications on his part). His past of being a military doctor is often correlated to his views of euthanasia, alongside the philosophy that "in nature, living creatures die they when they have to die." and counters Black Jack's views on "fighting death" by saying that "only humans try to prolong their own lives." in which he expressed his perspective to Black Jack in the film The Two Doctors of Darkness. It is interesting to note that he retains the pessimistic attitude on himself, as seen in the same film, asking Black Jack to abandon him to die when he received a gunshot wound, despite the lower chance of mortality on his part (being together with arguably the best surgeon in the world).
Kiriko is shown to have short hair in Episode 5 of Young Black Jack, usually seen in a military staff uniform accompanied with a helmet on his first encounter with the protagonist.
In volume 6 of Young Black Jack, he is seen with a short ponytail when he encounters a Vietnamese girl named Hoa.
Kiriko has a long white untied hair and has a pale skin. He wears an eye patch on his left eye and always walks with a grim face, just like Black Jack. He also even wears a black suit with a pair of black shoes to match and a long black coat. He was always seen carrying a large suitcase which is a special device that help Kiriko in his job to end someone's suffering life. Pinoko often mistake Dr. Kiriko for Black Jack in several occasions.
Before he became a doctor of death, he used to work as a military doctor once. He saw that many of his patients have no chance of surviving, thus he decided to help them die in peace by injecting them.
He works as the death doctor, travelling to any parts of the world, helping people to end their suffering.