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: Strange Journey
"One of the four oni controlled by Fujiwara no Chikata. Its body is so hard that no weapons can 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.