Blonde dude made red hair drink medicine that's supposed to turn a beta into an omega (telling him it was vitamins), made red hair forget a lot of things, even made him think that the person who kidnapped him was blonde dude (but blonde dude found him). This is the gist of it afaik.
I hope author is okay now. I remember she was sick with cancer i think?? Hopefully the return of this manhwa means since cancer-free now. She's one of the manhwa authors I read legally (I still go on mggo for the comments lol).

It's been so long, i don't remember the plot anymore lol