According to one theory, the descendants would experience a sound shift via ⟨*ima⟩, by */ʔimya/ → */ʔmya/ → */na/.[1] However, all reflexes point to initial *ena-ma > *ina-ma (second component identical to *ma(“place, space”)), with progressive palatalization operating in Northern Ryukyuan. Compare Proto-Ryukyuan*miyako > Miyako宮古(myāku) and Okinawan宮古(nāku).
This etymology is missing or incomplete. Please add to it, or discuss it at the Etymology scriptorium. Particularly: “See Talk -- the phonological shift from Proto-Japonic /*ema/ to Proto-Ryukyuan /*enama/ makes no sense: there is no /n/ anywhere in the Proto-Japonic, and no explanation for where this would come from.”