Here is the full list of all 48 Waifu Secret achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
1_Secret
2_Secret
3_Secret
4_Secret
5_Secret
6_Secret
7_Secret
8_Secret
9_Secret
10_Secret
11_Secret
12_Secret
13_Secret
14_Secret
15_Secret
16_Secret
17_Secret
18_Secret
19_Secret
20_Secret
21_Secret
22_Secret
23_Secret
24_Secret
25_Secret
26_Secret
27_Secret
28_Secret
29_Secret
30_Secret
31_Secret
32_Secret
33_Secret
34_Secret
35_Secret
36_Secret
37_Secret
38_Secret
39_Secret
40_Secret
41_Secret
42_Secret
43_Secret
44_Secret
45_Secret
46_Secret
47_Secret
48_Secret