Diving in Japan : Divers in Japan can explore reefs, caves and even glaciers

Article from Japan National tourism Organization

The Japanese archipelago offers incredible diving variety
Asian countries such as the Philippines and Thailand get more attention for their diving spots, but Japan offers all sorts of great opportunities too. You can find ice diving near the northern island of Hokkaido and tropical locations down south. You can also try out wreck or cave diving at famous landmarks like the Blue Cave off of the main island in Okinawa. For those looking to stay a little closer to the surface, islands such as Ishigaki have great snorkeling options, with colorful coral reefs and an array of sea life.

https://www.japan.travel/en/guide/diving/