Setsuna Kiryuu

Kiryu Setsuna, also known as The Beautiful Beast (美獣, Bijuu), is a mysterious individual whose history is closely intertwined with Tokita Ohma's. He was the affiliated fighter for the Koyo Academy Group during the most recent Kengan Annihilation Tournament. Two years after the Tournament, he suddenly reappears interacting with Gaoh Ryuki.

Kiryu was born in the Inside as organ stock for his wealthy biological father and spent his entire life beaten, detained, and unwanted. Before his captors harvested him, a young Tokita Ohma killed his captors because he believed them to be edging in on his turf. Believing Ohma to be a god that would destroy him for his sinful nature, Kiryu chased after him and remained within the Inside so he could find "god" again. Selling himself into child prostitution to gain money and connections, he soon earned the favor of one of the most powerful men in Goyu Ward. Going to the "Outside," Kiryu found and killed his biological father, stealing his money and using his connections to find "god" again. Two years after their first encounter, Kiryu learned of Ohma's location in the Inside and ran happily to his "punishment" only to find that Ohma had been "defiled" by the devil, Tokita Niko, Ohma's master. It was here that Kiryu met The Other Tokita Niko, who informs Kiryu about Tokita Niko as well as teaching him the Niko Style. Informed by The Other Niko about Taira Genzan, Kiryu later encountered the martial artist and became his student.

Two years later, Kiryu returned to the Inside[8] and found Ohma once again. Accosting Ohma, Kiryu forcibly activated the Possessing Spirit after it was bestowed upon him by The Other Niko, causing him to violently rampage. Ohma nearly killed Kiryu but was stopped at the last minute by the arrival of Tokita Niko. With Niko stopping Ohma's rampage, Kiryu then watched as Niko fought The Other Niko.

It was very soon after this that Kiryu's master Taira Genzan challenged and killed Niko when they were young. Then, during the ten years, Kiryu and Genzan fought in the Death Fights. In this time, before Ohma could exact revenge on Kiryu's master, Kiryu killed him first, intentionally earning Ohma's wrath.

(Source: Kenganverse Wiki)