660 years ago, the Kusanagi and Yasakani clans were once allies. However, due to a horrible misunderstanding, the Yasakani struck a blood pact with Orochi for more power. They renamed their family name to Yagami, and their flames, previously red like their former allies, changed to violet from Orochi's taint. Since then, the clans have waged a generation long grudge with casualties made from both sides. It continues in The King of Fighters series with Kyo and Iori Yagami.
The Orochi saga takes place between The King of Fighters '94 and 97. Kyo surpassed his father at the age of fifteen and was designated as the clan's leader. Shortly after the completion of his training, Kyo competes in a preliminary held in Japan to determine the members of the country's representative team in the King of Fighters tournament. He bests Goro Daimon and Benimaru Nikaido to become the leader of the team, the two becoming his teammates and eventual friends. They reach the finals, where they met the host of the tournament, a powerful fighter named Rugal Bernstein. Rugal boasts his desire to fight powerful opponents and challenges them. After his defeat, he self-destructs his ship in attempt to bring them with him, but the team escapes unharmed. Afterwards, Kyo decides to travel abroad in order to train.
In the following year, Daimon and Benimaru were waiting for Kyo's ship to dock, when they were attacked by a masked assailant. Kyo returns and throws a fireball at the mysterious person, only to destroy her mask and reveal her to be Rugal's secretary. She hands over an invitation letter to another King of Fighters tournament, organized once again by Rugal, who survived his craft's self-destruction. This time, Rugal also brainwashed Kyo's missing father, Saisyu, into attacking his son. Kyo's father regains his senses after he was subdued by the team. To counter the team's strength, Rugal challenges them with power sapped from Orochi. However, Rugal's body was overwhelmed by the power's immensity and he was vaporized after his defeat. Pleased with his son's prowess, Saisyu leaves unnoticed, insinuating that he entrusts the clan's duty to Kyo.
Prior to the events of The King of Fighters '96, a mysterious man -later revealed to be one of the "Four Heavenly Kings" of Orochi, Goenitz- challenges Kyo to a fight. Kyo arrives, powered by his overwhelming confidence in his fists, only to be defeated soundly by his challenger and sent to the hospital. In spite of his injuries, his anger and spirit from his loss drove him to invent powerful new techniques (this is the canon explanation for Kyo trading his projectile attack-based technique set for his now trademark flame-laced melee attack strings). He enters the year's tournament to prove his strength to his unknown attacker. In the tournament's finals, he meets the host of the tournament and the younger heiress of the Yata clan, Chizuru Kagura. At the tournament's end, he vanquishes Goenitz with Iori and Chizuru's help. Though he is warned by Chizuru of his clan's destiny with Orochi, Kyo ignores her and promptly departs.
Before The King of Fighters '97 takes place, he is pestered by fellow high school student, Shingo Yabuki, to teach him how to create his flames. Though annoyed and flustered by his persistence, Kyo partially agrees to mentor him as a means of gaining free meals. He also experiences nightmares of a strange man defeating him at the King of Fighters tournament, but continues to participate. Before the tournament, his girlfriend, Yuki was kidnapped by the Hakkesshu, in order to be used as the last of the sacrificial maidens for Orochi's revival. Though it's ambiguous as to which team he enters during the tournament, it is canonly accepted that Kyo joins with Iori and Chizuru for its conclusion.
He advances into the finals, where he confronts the remaining "Four Heavenly Kings" of Orochi, Yashiro Nanakase, Shermie, and Chris. The Hakkesshu also mention the plan to sacrifice Yuki in order to revive Orochi. Fueled by these turn of events, Kyo fights an emotional and heroic battle. When they are beaten, Orochi possesses Chris' body and attempts to destroy the three clans at once. As was done in the legends of their clans, the trio successfully defeat him. In a last-ditch effort, Orochi (manifested in Chris' body) causes Iori to enter the berserk Riot of the Blood state, expecting him to turn on Kyo and Chizuru. Instead, Iori snares Orochi by the neck, and Kyo obliged his rival by crippling the great demon with one last deathblow, allowing Chizuru to reseal Orochi. Exhausted, Kyo passes out. The last thing he sees is Yuki, saying that she will wait for him.
The King of Fighters '99 took place immediately after the events of The King of Fighters '97. Kyo was taken by the NESTS syndicate and his DNA was used to make various beings for their purposes. He awoke one day to find himself surrounded by bizarre gadgets and needles. Deciding to search for answers, Kyo broke out of captivity and managed to escape the hidden fortress despite the sedatives. While escaping, he constantly heard references to the NESTS cartel. He tries to personally gain answers from his captors, but is forced to retreat when the base around him begins to collapse. He decides not to come back home before NESTS is taken down and attempts to investigate privately again the following year but learns very little. As the fiasco of South Town's destruction ensued, Iori confronts him and they fight to an unknown outcome. In The King of Fighters 2001, Kyo reunites with his old teammates and Shingo to make a comeback in the Japan Team. They join the now NESTS-sponsored KoF tournament to relive their time together as a team and to fight NESTS. They disband as soon as the tournament is over, leaving Shingo to muse about life.
In The King of Fighters 2003, Chizuru appeared to both Kyo and Iori, requesting that they form a team and investigate suspicious activities concerning the Orochi. Kyo initially protested allying with Iori (though Iori apparently did not do likewise), but relented to form the Sacred Treasures team. After the defeat of Mukai, the team then investigated the weakening Orochi seal that they had been transported to before fighting Mukai, but were ambushed by Ash Crimson, who stole the power of the Yata Mirror from Chizuru, promising to go after Iori next. Ash escaped, and Kyo swore vengeance.
In The King of Fighters XI, Shingo has volunteered to join Kyo and Iori, in Chizuru's name. After several attempts, Kyo abides to Shingo's requests and joins forces with his groupie and his rival, in order to stop Ash. However, the growing presence of the Orochi (namely, the appearance of Magaki) caused Iori to snap and enter the Riot of the Blood state, and he trashed Kyo and Shingo in a berserk fit. Ash appeared thereafter and stole the Yasakani no Magatama within Iori's body, along with his flames. The Rival Team (Benimaru, Duo Lon, and Elisabeth Blanctorche) arrived after the incident, to whom Ash tells them that Kyo will be next.
The incident had Kyo hospitalized, but he escapes rather than wait for his recovery. As he wanders the city, he encounters a mysterious boy and his female partner, who try to attack him. Showing them his flames, they hand him the "R" invitation before taking their leave. Soon after the encounter, Benimaru and Goro find him. Seeing no need to visit the hospitalized Shingo or Chizuru, he reunites with his old team members to relive his past glory days together with them. After Ash disappears, Iori challenges Kyo once more to a fight. Though surprised to see Iori again with his flames, Kyo accepts and the rivals fight to an undecided outcome.
When the tournament was announced, Saisyu informs Kyo of a new threat which will cause untold chaos during the tournament. On his father's suggestion he convenes with Tung Fu Rue and a time-displaced Nakoruru to investigate while participating the tournament with his old teammates.
When his team wins the finals, Verse appears to wreak havoc and targets Shun'ei. They manage to defeat Verse but noticed the souls contained within had burst forth and scattered; one among those disbursed is Orochi. After the fight's conclusion, Kyo advices Shun'ei to keep training to control his powers. At the airport, Kyo tells his teammates to go home without him as Kyo has other business to finish. He arrives in Hungary after Chizuru calls him and helps to seal a weakened Orochi.