Jin is the leader of The Bounts, a group of immortal humans who feed off the souls of other dead humans, that is until Jin convinced them all to break their most sacred oath and consume the souls of the living in order to achieve Omnipotence.
Kariya orginally went by the name Eugene Currier, but later changed his name to Jin Kariya later on in life. Eugene as born a Bount,a group of mutated humans formed as a result of an accident in the Soul Society, which allows him to live forever as long as he consumes the reishi human souls.
Kariya made his presence known as the leader of the bounts when there were reports of people diappearing leaving only their clothes behind. in reality, these people had their souls consumed, and their bodies turned to dust as a result. he initally seeks to capture Uryu Ishida, to use his Quincy abilities to open a realm to the Soul Society to exact revenge on them for casting the bounts out. Kariya sought out the local scoundrels to help breach the seretei, and promplty betrayed them upon entry. In the Soul Soicety, the bounts had a battle advantage in that they could regenerate due to the reishi concentration, but all were eventuall defeated. Kariya had at one point absorbed a Jokai Crest, one if many which were used as energy generators, and were sealed away underground. he was planning to release the power to trigger the other dormant crests, but was stopped and defeated by Ichigo, while the seretei members re-sealed the other crests.
Unlike the other bounts, Kariya uses the wind as his doll, the ability which he received from Ran Tao.