Sea Hare (Aplysia japonica) クロヘリアメフラシ
There is a wide variation in color of Sea Hares, Aplysia japonica fits this one best. It was upside down in a cave, so I flipped the picture. Amami 2025
These Aplysia japonica were very close to the top one. I think that there were three of them. Amami 2025