If the Japanese aren't indigenous, nobody is. History talks about the "earliest inhabitants" of an area. If you go back far enough into history, you'll find that whoever "originally" owned some piece of land just isn't recorded. The "earliest inhabitants" didn't write down that their ancestor Ugh-Ugh the Lazy got Oogh-Ook of the Mountains drunk and hit him over the head to steal his valley. Ugh-Ugh didn't even know how to write.

If the Japanese aren't indigenous, nobody is. History talks about the "earliest inhabitants" of an area. If you go back far enough into history, you'll find that whoever "originally" owned some piece of land just isn't recorded. The "earliest inhabitants" didn't write down that their ancestor Ugh-Ugh the Lazy got Oogh-Ook of the Mountains drunk and hit him over the head to steal his valley, because Ugh-Ugh didn't know how to write.