Here is the full list of all 10 Beach Bounce achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Join Minami under the sea
Tame the wild woman that is Rei
Cheatings watery grave
Cheatings dark grave
Beat Aiko at her own game
Enslaved by a Succubus
Create a perfect love triangle
Have a happy if easy ending
Enjoy a nice end with Yuuki
Ruined your life over a round of drinks