According to the Kojiki, the "Records of Ancient Matters" complied in 712, the Oki Islands were the third island created by Izanagi and Izanami, after Awaji Island and Shikoku Island, and were recorded under the name Oki-no-mitsugo-no-shima (the “Oki triplet islands”), a.k.a Ame-no-oshikorowake. Also, according to Nihon Shoki, the "Chronicles of Japan" compiled in 720, Oki and Sado Island were born as twins.
The fact that the Oki Islands were treated extensively in these documents suggests that the imperial court back then considered these islands as crucial, and one of these reasons is believed to be obsidian. Obsidian mined in Oki were mainly circulated in Chugoku region from 30,000 years ago. People and culture interacted through the obsidian trade, and it can be seen that Oki prospered from prehistoric times to ancient times.