Just to clarify where the story is at right now...
The joke is that MC Alpha thinks that the blondie Omega is the same girl she hooked up in the first 2 chapters, when in reality that was her twin sister (who is also an Omega)
(I have a hard time following the story, but the only hint is the phone screen with big sis in previous chapter, am I getting it right that ever since that one night stand, the blonde girl MC met is different from the original one, the entire time? or were they swapping other times and I didn't notice)