This is the Solution for these Guys who are not able to get Achievements!
1. Deinstall the Game.
2. Close Steam completely (stop the Prozess!).
3. Delete these 2 Folders:
...\Steam\steamapps\common\one night, hot springs\onsengame-market\game\saves ...\AppData\Roaming\RenPy\onsengame-1517489131
4. Start Steam.
5. (Re-)Install the Game.
6. Play the Game.
7. Enjoy the Achievements!