Writing in the Ryukyu Kingdom
The Ryukyu Kingdom (1372–1879) on Okinawa Island used various writing conventions, all of which were markedly different from spoken registers. A unique feature of Ryūkyū's writing conventions is that in the Old Ryūkyū period (? –1609), it developed a predominantly kana writing convention that was based on sōrō-style Written Japanese but exhibited heavy Okinawan influence.
Source: Wikipedia — Writing in the Ryukyu Kingdom (CC BY-SA 4.0)