mainlander; person from the mainland
Refers to someone from the main islands of Japan, often used in contrast to people from Okinawa or Hokkaido. Neutral term, but context may imply a distinction from local populations.
To people in Okinawa, mainlanders can sometimes seem to have a slightly different culture.
He is a mainlander, but he has completely gotten used to life in Hokkaido.
Compound of 本土 (mainland) + 人 (person). The term is straightforward and modern.