Is nihonjin japan sun, or japn water, or japan spirit?

Question:

What japan human is?

Answer:

I am not sure what you are asking but,
nihonjin (日本人) means Japanese person, and is written with the kanjis of sun, book (origin, in this case) and person/human. It comes from 日本 (Japan, literally:sun-origin) and 人 (human/person).
You can add 人 to any country's name to make a noun for person/human from that country in Japanese.