Hyakka is the eighth son of the Otori family, a prominent fire-wielding clan with roots stretching back over nine centuries. When his older brother died, he was brought into the Goko Clan as a replacement. Like Mao, he hails from the Heian Period, though he joined the Goko Clan ten days earlier—a detail Mao never lets him forget, addressing him formally as "Lord Hyakka."
He's known for being cocky and blunt, quick to voice his opinions without much filter. His fire abilities come with a major weakness: water users like Mokuzu and Shiranui can neutralize his attacks entirely. During the infamous Five-Sided Room incident, Hyakka was one of several assassins sent to kill Mao, though the screens separating each side kept everyone's identities hidden. That changed when Hyakka made an impulsive outburst that gave him away to the others.
Over the centuries, he's drifted through various jobs—carnival performer, ramen cook—keeping a low profile like Mao, both having gained immortality somewhere along the way. Everything changed in the 1920s when his past started catching up with him. He'd always blamed Mao for Sana's death and suspected him of stealing Byoki's powers, but he eventually learned the truth: Mao had been framed in an elaborate conspiracy going back centuries.
In the early 1900s, Hyakka ran into Hakubi, a metal user from his past. Fire should've given Hyakka the clear advantage, but they fought to a draw—though not without damage. Hyakka left Hakubi badly wounded, and Hakubi managed to cut out Hyakka's eye in return. What Hyakka didn't know was that Hakubi resented him deeply, convinced that Hyakka's place in the Goko Clan was pure nepotism and that he didn't deserve it.
Content compiled by AnimeList.moe from publicly available sources.
