Riot of the Blood

The Riot of the Blood (血の暴走, Chi no Bōsō, lit. Rampage of Blood) is a fictional physical and psychological transformation that appears throughout the The King of Fighters series fighting games. It was first shown in The King of Fighters '96.

Overall
The Riot of the Blood is a circumstance that affects individuals with partial Orochi ancestry in their bloodlines. This condition happens when outer influences or an event makes the Orochi blood in a person resist their normal blood. In most common instances, those afflicted go completely berserk. Those with full Orochi blood are not affected by this uncontrollable state. Orochi and his followers can directly trigger this within themselves and others. All individuals will undergo minor physical changes (notably in hair color and skin tone) and become more resilient to pain.

Users

 * Chris of the Flames of Destiny
 * Yashiro Nanakase of the Parched Earth
 * Shermie of the Insanely Violent Lightning
 * Wild Iori, inherited from the Orochi-cursed Yagami bloodline.
 * Wild Leona, inherited through her father.
 * Aoi Kusanagi (never entered the state, but is susceptible to it)
 * Everyone of Yagami (Yasakani) heritage.

Non-users

 * Leopold Goenitz uses wind, and in his seemingly normal state, is known by his Four Heavenly Kings title without the transformation Chris, Yashiro, and Shermie must undergo. It is unknown if he is already in his form, simply does not require being in this state, or if he is even capable of entering Riot of the Blood. He is, however, capable of triggering it within people.
 * Vice, Mature, and Ryuji Yamazaki are also Orochi's "heads" and represent said elements, but do not enter the Riot of the Blood state as the Four Heavenly Kings do. It is worth noting also that these characters are especially violent without the Riot of the Blood.

Trivia

 * During Iori's SDM Ya Otome, he will go into this state and begin viciously mauling his opponent, before smashing his arms on them to emit the signature purple fire explosions. This only happens in games that involve the Orochi's prescene being about before the end of  '97 however, such as during the whole Orochi saga, and during the NESTS saga Dream Match games (where in both  '98 and 2002 's cases, most and in some cases all of the Hakkesshu members are alive).
 * The only exception to this is KOF XIII, where both Mature and Vice take the form of phantoms, and Iori happens to be free from his curse as his flames were stolen. However, EX Iori despite having his flames unlike normal Iori is not susceptible to the state in his EX Ya Otome, even when he shows some signs of it during his Homurahotogi/En'ou Neo Max (ripped from his original MAX2/HDSM).
 * Leona is the only character in 2002, Neowave and 2002 Unlimited Match to enter this state through a move, costing half of her total health in exchange. She enters this state as well temporarily in KOF '98, KOF '98UM and canonically, KOF XIII in either her Neo Max and SDM move. It suggests that Leona is gaining complete control on using Riot of the Blood to her advantage.
 * However, in some circles like the M.U.G.E.N. games, Iori can also enter his Riot of the Blood state by the same type of command (which also costs health like Leona's method). The only time Iori has demonstrated such control over Riot of the Blood was by entering the state temporarily in his SDM in KOF '98, KOF '98UM, KOF 2002 and KOF 2002UM, all which are dream matches and not canon; this is also somewhat barring the use of his aforementioned En'ou/Homurahotogi via its portrayal in KOF XIII.