Long ago, the Japanese had different names for each of their islands within the archipelago. Completely different names from what we now call them. The main island (now called Honshu) represented...
No. It is just like the English Channel is not part of England. It lies beneath it but it is not actually owned by them. They share a partnership with France (secretly)
It's east sea from Korea. There is Korean protectors in the island called dokdo and it is the island that decide whose sea it is. Historically it is Korean sea