Here is the full list of all 26 Senpai Puzzle: Waifu Summer achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
10 Waifus Collected
9 Waifus Collected
8 Waifus Collected
7 Waifus Collected
6 Waifus Collected
5 Waifus Collected
4 Waifus Collected
3 Waifus Collected
1 Waifu Collected
2 Waifus Collected