Preliminary reports have it as a DCH-8. It is a 50-70 seat twin turbo prop. Not sure how it would be configured for the JCG..
Thanks
More here...
https://mainichi.jp/english/articles/20240102/p2g/00m/0na/026000c
Per Mainichi, the captain managed to escape the CG plane.
According to wikihahahapedia, the Japan Coast Guard has 8 (minus 1) Dash-8 aircraft outfitted for maritime surveillance. That means they’re loaded with electronics, not passengers.