I'm not a Greek speaker, although I know a few roots and a little grammar.

"Galaxy" is indeed Greek; not surprisingly, the ancient Greeks called the strip of dense stars part of the galactic plane the "Milky Circle". Of course, they did so in Greek: galaxias kuklos. (Greek gala, "milk" is probably non-IE, possibly Old Mediterranean).

Akatsukami is in fact an archaic Japanese word meaning "incarnate deity" (used to refer the tenno (emperor)); in modern parlance, I believe one would say aramikami. How it to be applied to me is an only marginally interesting story involving a naïve young financial analyst and a guy who wanted to pose as a C programmer.

Frankly, I can't think of any reflexes of mundus in English save "mundane".