Koropokkuru are a race of small people in Ainu folklore. The name is traditionally analyzed as a tripartite compound of kor or koro ("butterbur plant"), pok ("under, below"), and kur or kuru ("person") and interpreted to mean "people below the leaves of the butterbur plant" in the Ainu language.
The Ainu believe that the Koropokkuru were the people who lived in the Ainu's land before the Ainu themselves lived there. They were short of stature, agile and skilled at fishing. They lived in pits with roofs made from butterbur leaves.
Long ago, the Koropokkuru were on good terms with the Ainu, and would send them deer, fish and other game and exchange goods with them. The little people hated to be seen, however, so they would stealthily make their deliveries under cover of night.
One day, a young Ainu man decided he wanted to see a Koropokkuru for himself, so he waited in ambush by the window where their gifts were usually left. When a Koropokkuru came to place something there, the young man grabbed it by the hand and dragged it inside. It turned out to be a beautiful Koropokkuru woman, who was so enraged at the young man's rudeness that her people have not been seen since. Their pits, pottery and stone implements, the Ainu believe, still remain scattered about the landscape.
"Small human-formed demons from Ainu legend. Called "One that lives under Fuki", they are considered to have a kind, calm personality. Once coexisting with the Ainu people, there was a falling out at some point and it is said they simply disappeared. They were believed to have inhabited Hokkaido even before the Ainu."
—Devil Summoner: Soul Hackers compendium
Devil Summoner 2: Raidou Kuzunoha vs. King Abaddon
"A small, human-shaped demon of Ainu legend, it is believed to have a calm, kind disposition. Though they once coexisted with the Ainu, at some point there was a scism and they simply disappeared."
—Devil Summoner: Raidou Kuzunoha vs. King Abaddon devil chart
"Small human-like creatures, that have kind, calm personalities. Once coexisting with the Ainu people of Japan, there was a falling out at some point, and they disappeared."