In ancient times the Yasakani (Yagami) Clan was tricked into making a pact with Orochi to gain veangance upon the Kusanagi Clan (framed for murder of a Yasakani family member). As such all Yasakani/Yagami clan members are prone to short life spans and the mothers die in childbirth.
Iori's Riot of Blood is first activated by a dying Goenitz who exacts revenge on Mature and VIce for betraying him at the end of the 1996 King of Fighters Tournement. His Riot of Blood is activated in 1997 by Orochi himself but Iori manages to use his enhanced physical abilities to help defeat Orochi and seal him away again.
In this state, Iori goes into a blood thirsty rage in which he can only speak and few words. He physically becomes much faster and more powerful, with a drawback of very low defense. Orochi Iori is sometimes referred to as "Riot Blood" Iori or Wild Iori, and is often a hidden character in the King of Fighters franchise, much like Shin Akuma is to the Street Fighter franchise.