Adult PC Game: In the Aquarium: Sinking with Kana by FoxEye Archive

A spin-off work of "Karin's Skin Diving Diary!".
The school swimsuit-wearing protagonist Kana has an adventure as she dives into a tank at the aquarium.

While the genre is illustration collection, you can follow the story and get branching paths, for an adventure game feel.
But for those who simply want to see the CG, of course, there is no save data and all the images are there from the start for you to enjoy.