I always found the Sengoku period in Japan extremely interesting to me, and I just recently found out my grandmothers family is from the tiny Island known as Okinawa. So, uniting both my interest in the Sengoku period and my heritage I come to you with this exact question.
I researched online about this topic extensively and I seriously could not find much at all about this specific question. Obviously Okinawa is very far away from Japan, but I did see mentions of them having contact with the Wako whom were Japanese I believe. If the Okinawan's did have any contact with mainland Japan, what was it?
I'm fully aware of how extremely specific this question is, and I understand if there are no sources for this question. Although, I would be very appreciative if any of you Japanese historians do have any sources regarding the Okinawan's and Japanese contact with each other!
During the Sengoku period both China and Malaysia had a greater influence on Okinawa and the other Ryūkyū islands than Japan did. Only in the Edo Period (1603-1868) did the Japanese gain more influence, as they invaded the islands and made it a tributary. Ryūkyū remained an independent nation and had a formal trading contract with the Japanese only after the invasion during the Edo-Period.
The Ryūkyū Islands became a tributary of China in 1372, consequently they were allowed to trade in Ming ports. Their trade partners did in include Japan. Trade is the biggest influence Japan had on the islands during that time, as they traded their silver, weapons and interior design like folding screens and tatami mats. During the 1500's they were also plagued by wokou, which are Japanese pirates.
In the late 1500's (around 1590) Hideyoshi sought help from Naha (capital of Okinawa) to help the Japanese invade Korea due to the advantageous position of the islands. They declined. In the following years the Shimazu family, lords of Satsuma in Kyushu, who had a history of trading with Ryūkyū, threatened the Ryūkyū kingdom into submission and demanded an embassy of tribute. They declined again until the invasion in 1609.
Sources: George H. Herr, Okinawa, p. 155: Shin'yashiki Yukishige, Shinkou Okinawa issennen shi
Ronald P. Toby,State and Diplomacy in Early Modern Japan. Asia in the Development of the Tokugawa Bakufu, p. 40 ff: Princeton University Press
Chōshin Higa, Okinawa sengoku jidai no nazo: Nanzan Chūzan Hokuzan Kumejima Miyako Yaeyama