Where does “Takamagahara” come from?

Takamagahara (English) comes from Japanese 高天原, from Japanese 高, from Middle Chinese 高.

Ancestry of “Takamagahara”, step by step

Step	Language	Word	Meaning
1	Japanese	高天原	the sky, heavens; the realm of the gods; "Same...
2	Japanese	高	maximum, the limit; high, higher
3	Middle Chinese	高	—

Takamagahara — Etymology, Origin & Word History | Etymology Explorer