Kayin Amoh made his first appearance in Battle Arena Toshinden, as an initially playable character. He also appeared as an initially playable character in Battle Arena Toshinden 2, 3 and the Japan only spin-offs Puzzle Arena Toshinden and Toshinden Card Quest.

He is a friend of the series' main protagonist Eiji Shinjo and is described as being a bounty hunter, going by the name of Storm. He was trained in swordfighting along with Eiji by Eiji's older brother Sho, until he suddenly disappeared. Kayin then entered the first Toshinden tournament to avenge his father's recent death, who he learned had been killed by a participant who won the previous tournament. He eventually learned that Sho was the perpitrator and his friendship with Eiji was nearly shattered because of this.

Kayin was then forced to enter the second tournament after his adoptive daughter, Naru, was kidnapped by the Secret Society. At the end of the event, he managed to help bring down the fall of the Secret Society and rescue Naru. However, he then discovered that they were being targeted by the Organization. He participated in the third tournament hosted by it and managed to help destroy the Organization. However, he realized that Naru would always be in danger because of him and he decided to leave her in a housing institute. He handed down his Excalibur sword to her and then disappeared.

Source: Wikipedia