This is a fairly common alternate universe (AU) in fanfiction. Not quite as common as the Hogwarts AU, but still quite a common trope, regardless of the fandom. Doubtless, I've mentioned it before - but I'll give you a refresh.
Omegaverse dynamics work a bit like a wolf pack (or, that's the theory anyway.) Alphas are in charge. Betas faff about in middle-class status.
Omegas are typically the weakest, the rarest, the most beautiful, and the most fertile - regardless of gender. Whether women can be Alpha depends on the author's preferences.
MPreg (male pregnancy) is common in this AU, and breeding is determined by animalistic 'heats' - which, as can be imagined, cause a heap load of problems.
The other thing about this type of fanfiction is that there is always sex at some point (which is the case for a lot of fanfiction really) - it can get pretty weird.
Some people have thought how this works through to a
I am also not explaining knotting. Because I don't know where I'd start. Let's just say there is... bonding... and... glands.
Every fanfiction author has their own rules and variations to the Omegaverse theme - for example, whether there are suppressants which can stop a heat, the rights of Omegas, whether families literally live in 'packs,' etc. It can actually lead to some pretty interesting stories.
This week's fic makes use of Omegaverse (otherwise I wouldn't have just spent a good chunk of my time explaining it to you,) in this version of the AU, there are 'Hunters' - who can recognise an Omega before their first heat (which is when, usually, orientation is revealed.)
Lost Brother by thunder_from_asgard
- is a Thorki Omegaverse fic. I explained Thorki here - basically, Thor and Loki are together romantically. This is fanfiction - just go with it.
I should mention at this point that I recommend this as 18+ Only - I know you might ignore me, but I owe it to myself to try and warn you. There's sexual slavery, and a bunch of trauma and sexual assault in this story, so please reader, beware.
Now that that's all said - I can tell you that this is a relatively long fic, at 11 chapters, and is, actually, very good.
Again, when it comes to fanfiction my perception has become a bit warped by the amount of the stuff I've actually read. For example, I'm no longer surprised by MPreg, or Omegaverse in general. My view of 'normal' is becoming increasingly blurred.
But I do think this fic is worth the read - it's interesting, really considers the emotional fallout of events, and is quite well-written.
There are spelling and grammar issues - but the author is not a native English speaker, and if I wrote this well in a second language, I'd be pretty damned proud of myself.
So, there you have it; Omegaverse. Just another randomly compelling facet of the bizarre world of fanfiction.