"One of the four oni Chikata Fukiwara was said to have controlled during the Heian period of Japan. His body was so tough, swords and arrows bounced off of him."
—Shin Megami Tensei III: Nocturne compendium
Kin-ki is one of four optional bosses that can be fought in the Ikebukero Tunnels. During the fight, he will regularly cast Beast's Eye, followed by a buff or debuff, and ending with a physical attack, such Blight or Hell Thrust. Once his health reaches a low enough point, he will switch to Dragon's Eye. For this battle, it is recommended to bring demons with Dekaja and Dekunda to counteract his strategy
Kin-Ki can only be obtained through fusion. He appears as a field boss on Shinjuku field when summoned by one of the charms the Yaksini NPC in Ichigaya Camp's B11 will trade for magnetite. A strengthened variant called Peerless Steel-Bodied Kin-Ki can be fused by players after completing a series of G1 Trial quests from a Cathedral of Shadows researcher in Ikebukuro. This variant learns the unique skill Lightning Flash Massacre.
Kin-Ki is the sub-boss faced at the end of the Challenge Quest, I Want to Make the City Bright. He has created a Domain over a relic spot in Ueno - Central Way and must be defeated to obtain the LED Lightbulb. He can be refought for the item he has after a certain amount of time has passed.
"One of the four oni controlled by Fujiwara no Chikata, its body is so hard that no weapons can penetrate it."
—Persona 5 background
Kin-Ki is the fifth Persona of the Chariot Arcana and can be found as a Shadow in Kaneshiro's Palace as mid-bosses and regularly as a normal encounter in the Kaitul area of Mementos, with the title “Demonic Warlord” in the vanilla version and "Samurai Killer" in Royal. Kin-Ki is one of two Personas to learn the Vajra Blast skill and one of three Personas to learn the Regenerate 1, Dodge Psy, Sledgehammer and Bad Beat skills. When itemized through Electric Chair execution in the Velvet Room, Kin-Ki yields a Regenerate 1 skill card.
Kazuma Kaneko did not intend Kin-ki to use any weapon, unlike his fellows. But likely for saving an individual set of skeletal animations, his 3D model is given the same club of Oni and uses the same attack animation. This design decision continues to Persona 5, when all 3D models and animations were given a revamp.