Nipponese vs Ryukyuan

Nipponese and Ryukyuan both are nouns.

Word	Noun	Adjective	Verb	Adverb
Nipponese	Yes	Yes	No	No
Ryukyuan	Yes	No	No	No

As nouns, Ryukyuan is a hyponym of Nipponese; that is, Ryukyuan is a word with a more specific, narrower meaning than Nipponese:

Nipponese: a native or inhabitant of Japan
Ryukyuan: a member of the Japanese people living on the Ryukyu Islands southwest of Japan

Other hyponyms of Nipponese include Jap, Nip, geisha, geisha girl, shogun.

Nipponese (noun)	Ryukyuan (noun)
a native or inhabitant of Japan	the language (related to Japanese) that is spoken by the people of the Ryukyu Islands
	a member of the Japanese people living on the Ryukyu Islands southwest of Japan

Nipponese (adjective)	Ryukyuan (adjective)
of or relating to or characteristic of Japan or its people or their culture or language