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.
Create a perfect love triangle
Join Minami under the sea
Enslaved by a Succubus
Cheatings watery grave
Cheatings dark grave
Tame the wild woman that is Rei
Beat Aiko at her own game
Have a happy if easy ending
Enjoy a nice end with Yuuki
Ruined your life over a round of drinks