$HOME/Library/Application Support/com.HuniePot.HuniePop2-DoubleDate/ .
To use a downloaded save file, you must manually move it into the game's local data folder. huniepop 2 100 save file link
Reaching 100% achievements requires replaying the game 3 times to pick different rewards from Kyu after the final battle. Steam Community secret codes for specific outfits or hidden achievements? Guide :: HuniePop 2: Double Date saves - Steam Community $HOME/Library/Application Support/com