Here is the full list of all 20 Peeping Dorm Manager achievements. It takes around 5-6 hours to unlock all of the achievements on Windows.
Obtain all of Uehara Mirai's CGs
Obtain all CGs
Obtain all of Akizuki Misaki's CGs
Learn all skills from the gentleman club's instructor
Fully dominate Uehara Mirai
Collected all of Misaki Akizuki's panties
While playing the plumbing mini-game, reach a full SSS combo
Fully dominate Takanashi Otohime
Fully dominate Miss Mango
Purchase all products from the supermarket clerk
Collected all of Mirai Uehara's panties
Fully dominate Akizuki Misaki
Fully dominate Kinoshita Yuri
Purchase all products from the gentleman club's manager
Successfully enter Misaki Akizuki's room
Get taken away by the police
Successfully enter Mirai Uehara's room
While playing the trash sorting mini-game, reach a full SSS combo
While playing the cleaning mini-game, reach a full SSS combo
Successfully complete the tutorial.