The King of Fighters has had multiple story arcs over its main 15 entries thus far. However, the original arc is still one of the most beloved by many fans. It ended over 25 years ago, so there are people who may have never heard of the original Orochi Saga in The King of Fighters - which includes King of Fighters '94, '95, '96, and '97.
As the story goes, in ancient times there was a being named Orochi; the guardian of nature which maintained balance between the world and humanity. However, as humanity grew in power, its destructive force angered Orochi, and the diety decided to wipe humanity from existence. Orochi’s followers, known as the Hakkesshu, waged war with humanity until they were defeated by the Kusanagi, Yasakani, and Yata clans.
Hundreds of years later, an ancestor of the Hakkesshu killed the wife of the Yasakani leader and framed the Kusanagi, driving a rift between the two clans. The Yasakani clan made a blood oath with Orochi in order to get revenge, and renamed themselves Yagami. The Kusanagi and Yagami clans fight through to the modern day while maintaining seals to Orochi, opening up into the plot of SNK's popular series.
The King of Fighters '94 and '95
In the first game, Goenitz - the new head of the Hakkesshu - seeks to revive Orochi. Believing arms dealer Rugal could be used as a host for Orochi, he sends Vice and Mature to observe him. Rugal hosts the tournament in The King of Fighters ‘94 to grow his “collection” of living statues based on people he’s defeated. Heidern, an operative eager to get revenge after Rugal killed his wife and child, joins with his Ikari Warriors operatives. Ultimately, the Japanese team wins and defeats Rugal, who fails to kill them all by blowing up his ship.
Rugal survives the explosion and decides their victory was a fluke, hosting a new King of Fighters tournament. All previous teams join except the American Sports team, who have their invitation stolen by a new Rivals team. The Japanese team wins again and faces Rugal, who taps into the Orochi power given to him by Goenitz. He is defeated again and dies trying to utilize more of the Orochi power. Elsewhere, Iori of the Yagami clan violently attacks his teammates after their defeat, vowing to kill Kyo and the entire Kusanagi clan.
The King of Fighters '96
Some time after Rugal’s death, Kyo is challenged by Goenitz, which he loses and is nearly killed. A new tournament is held by an unknown source, in which Iori teams up with spies Vice and Mature. Heidern decides to observe from the sidelines, and introduces his adoptive daughter Leona to the Ikari Warriors.
The Japanese team wins again, and the tournament host is revealed to be Chizuru Kagura, the new priestess of the Yata clan after her sister was killed. Before she can explain what’s going on, Goenitz appears and destroys the stadium. He attempts to take out all three clans at once, but Kyo, Iori, and Chizuru defeat him. Humiliated, he kills himself.
The King of Fighters '97
The King of Fighters tournament has become so popular that a new edition is announced. Chizuru joins the Women’s team, hoping to team up with Kyo and Iori again, and a "New Faces" team composed of members of the band C.Y.S. join to get revenge on Iori after his jazz band replaces them at a club.
Iori joins as a solo contestant, haunted by the ghosts of Vice and Mature after he murdered them under the influence his clan’s curse: the Riot of the Blood. Leona also suffers from this curse and is revealed to be a Hakkesshu who killed her entire village after Goenitz awakened her Riot of the Blood. The New Faces team is later revealed to be trying to revive Orochi. Eventually, Orochi is revived with Heavenly Kings member Chris as a surrogate body; his teammates Yashiro and Shermie as energy sacrifices.
Orochi tries to defeat the Sacred Treasures team, but they prevail. Desperate, Orochi enacts the Riot of the Blood in Iori, expecting him to attack Kyo and Chizuru, but he turns on Orochi. Kyo then delivers a final deathblow and Chizuru seals Orochi again. Kyo disappears for over a year and the Hakkesshu, except Leona, are exterminated, setting up future arcs in King of Fighters games after the tournament goes into hiatus.