Kin-Ki is one of the four oni controlled by Fujiwara No Chikata. Named after gold, Kin-Ki's body is so strong that no weapons in existence can pierce it.
"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
Shin Megami Tensei IMAGINE
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.
Shin Megami Tensei: Strange Journey
"One of the four oni controlled by Fujiwara no Chikata. Its body is so hard that no weapons can penetrate it."
—Shin Megami Tensei: Strange Journey Compendium
Shin Megami Tensei IV
Kin-ki is the 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.
Kin-ki later appear as normal enemies in Infernal Tokyo.
Persona 4
"One of the four oni controlled by Fujiwara no Chikata, its body is so hard that no weapons could penetrate it."
Requests Macca. After using on the same clan of demons thrice, any demon of that clan will take away one third of player's Macca forcefully in the next encounter.