Kariya Kagetoki is an elite samurai working for the Shogunate known as the "Divine Hand" and "Hand of God" because of his skills in combat. Being said that there is possibly no one in existence capable of defeating him, he is arguably the strongest fighter in the series. According to Goroujuu, a Shogunate member, Kariya has not drawn his sword in quite some time since there hasn't been a worthy opponent in years.
Kariya has traditional chonmage hairstyle from the Edo period and a circle beard. When fighting, he wears a straw hat.
Kariya has a calm and collected demeanor that hides a cold and manipulative personality. He has gone into retirement because there wasn't a single worthy opponent for him and he does gardening in his pastime. He has a sense of honor (as we've seen when he let Seizo Kasumi say his final words to his daughter), and he also gives praise when he's impressed (showcased when he complimented Mugen's style and Jin's skills in swordsmanship as well as when the latter survived his fatal strike).
He was very analytical when fighting Jin and Mugen, understanding Mugen's unorthodox style and warning that his instinct and reflexes will limit him and he tells Jin that the battle will be decided by a razor thin margin. Kariya acknowledges the fact that a samurai cannot live by his sword skills alone and that the age of the samurai era is ending, displaying worldliness.
He did agree with Jin's opinion, that the Lords of their time value only themselves and not the lives of their employees and admits that while he's in fact working for the shogunate, he's far from being any man's puppet, on the contrary, he's the one who uses them.
Not much is known about Kariya's past. He was working for the Shogunate and he had attempted to gain control of the Mujushin Dojo and is the one responsible for ordering Mariya Enshirou to kill Jin. He is ordered to seek out and eliminate Kasumi Seizou, the Sunflower Samurai, for his role in the Shimabara Rebellion as well as Kasumi's family — Fuu. He learns of Sara's death from Goroujuu while gardening and therefore decides to draw out his sword and face his enemies, viewing them as worthy adversaries.
He meets up with Mugen and Jin and lets them know that the Shogunate is well aware of their journey to meet Kasumi hence they must die by his hands. He demonstrates his so-called godly abilities and proves to be too strong for the pair. Like Shōryū, he's master of his ki and is able to use it with great force both offensively and defensively, and to an almost supernatural level. When Mugen leaves after hearing about Fuu, Jin is fighting him alone. The two exchanged ideals about the world before eventually Kariya had emerged victorious and gone after Fuu.
He arrives at Kasumi's residence killing him instantly after the latter talked to his daughter and then Kariya admits that all relatives and retainers have to die as well. After Kasumi's caregiver, he attempts to kill Fuu at a cliff, but Jin arrives revealing that he's alive. They had their final fight and it seemed that Kariya had won, but utilizing a suicidal strategy that his master taught him, Jin defeats Kariya.