With some Jircniv x Ainz on the side for the shippers . We are also just going to assume Momonga started playing shortly after his mothers death at 12 as a way to cope so he ends up being 24 which is only 2 years older than his soon to be boyfriend/husband . Also if you haven't read “Undead Embrace" on ao3 i strongly recommend you do now .
With Momonga as the (very brooding) sole parental figure of Nazarick
Who just happened to a Omega
In a word in which secondary genders other than Beta are rather rare , how rare you might ask . Around the same spawn rate as gen 1 shiny aka technically a lot of them but the normal human happening upon them being extremely low , though some races have higher chances of people being a secondary gender other than Beta
Other people in Nazarick presented as non-Beta , more specifically one of the 3-4 people being Albedo(Omega) , Cocytus(Alpha) , Pandora Actor (Enigma(as in having characteristics of both Alpha and Omega)) and Sebas (Alpha)
And A/B/O dynamics didn't exist in neither YGGDRASIL or Momo's og word ... So yeah this is totally new territory for all of them . And then there is underlying sexism of Omega being discriminated against for being seen as weaker and often kidnapped or sold into sex slaves (at least with humans) . Yeah … Nazarick is gonna crash out the moment they learn of that side of slavery and demolish it , mainly because they see it as disrespect to their master . It does at least result in the Sorcerer Kingdom having very strong laws in the protection of Omegas and giving them the same rights .
Anyway let's go with at least some of the things happening in canon and how the new worders react to … well a freakishly strong Omega .
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We start with Gazef who probably had the strangest meet up . Because the 2 people he met weren't just 2 Omegas (one of who is a powerful caster and the other what he assumes a rather strong warrior ) , but one of whom smells like a just freshly presented Omega (it's Albedo) , which is strange considering both of them look to be full adults . He isn't really questioning it , and considering the fact Ainz is a powerful magic caster he just assumes Albedo is his daughter who decided to take the warrior path maybe like her other parent . When he gets back to the capital and report the vast majority of nobles don't believe him because in their puny brains the thought of an Omega being so capable is impossible
Then we have the adventuring with Momon and Nabe , who are confusing everyone (in part because of how interwoven their smells are from the constant cuddling Ainz does with those from Nazarick as his new instincts dictate) . Mainly because before Ainz took the helm down everyone thought he was a freshly presented Beta noble brat with an Omega companion . Then the sword of darkness happened and having observed those 2 people come to the conclusion that Nabe is a freshly presented Omega and Momon is her Beta Parent trying to stop her from cawing peoples eyes out . Then as they continue and notice that Momon parents in a way very similar to an Omega so they think there must have been an omega in his village in like the last 3 generations (when an Alpha or an Omega are born normally villages will start to slightly revolve around them resulting in changes in culture) , except the longer they look the less it seems like that and more so that Momon is an Omega parenting his Beta daughter . It's understandably a shock to have an Omega be a warrior and not a mage when they go into combat professions . In whatever case the fact that Momon is old enough to be Nabe’s parent becomes public knowledge . And while at first people are disgusted and tink that Momon is as bad or at least close to to the 8 fingers in that they take advantage of young girls , except the longer they look the less and less that misconception makes sense and the more and more obvious becomes the fact he is trying to parent and reign in a child able to use tier 3 spells along with being able and willing to maul a person alive with her teeth alone . At first they think “Ah , that is his daughter” , however Nabe’s polite tone when talking to him and the fact she sometimes accidentally adds in “lord” makes people suspicious that they might be from nobility , along with raising the suspicion that either they weren't originally close all that much(has they been then she would have relatively little problems calling him just father rather than lord father) or he had not been her parent figure from the start (some children might still call their adopted parent by their first name even if they do see them as their parental figure and have been for years) . Then Momon lets loose that Nabe is the daughter of a precious friend of his and how she is one of the very few things he has to remember him by . And suddenly it clicks . Momon was obviously a very high ranking knight(probably a situation similar to Gazef) that served his friend who was a king of a nation , however something happened and his friend is dead and his daughter is one of the few things he has left from him(she might be the only heir or at least the friend's only child) however she wasn't safe in her home country for one reason or another (scheming family , women not being recognized as rulers , a successful coup that would make her an unwilling bride so the traitors can claim legitimacy) . So instead Momon took her and they fled the country , all the while he tried to make money the best way he knew by selling his sword and with Nabe learning magic along the way(or maybe while she was still a princess) . Until they came here and became adventurers . That's how the titles of “Princess Nabe” and “Raven Black Hero” came to be . Eventually it would come to light that Momon is the Omega and not Nabe but that doesn't really change anything anymore but it does add some sense in why Nabe is so protective of him and why when camping or generally being around other people the 2 stay together but move away from other people as you have 1 very beautiful and talented mage Beta and her equally if not more attractive(as described in the lightnovels strength is very attractive) Omega step parent .
However even with Momon as the most attractive person most people have ever met in their lives the fact remains that 1) he hasn't shown interest in neither sex or romance as demonstrated by his lack of interest in Evileye or any of the dozens of adventurers that have thrown themself at him and 2) his daughter will try and kill if you even try to date him . It definitely makes the scene of Momon , Nabe , Albedo and Ainz all the more hilarious as you have 3 monsterously strong Omegas in one place deciding what might be the fate of humanity and as a cherry on top the only Beta present isn't even the warrior but a mage .
Anyway we continue . The lizard man arc stays mostly the same other than them wondering why Ainz hasn't taken Cocytus as his mate , because in lizardmen society a Omega and Alpha are always expected to end up together no matter what (that's actually why they were lowkey surprised when Crush and Zenbery didn't immediately end up together but instead only got together when Zaryusu was included in the trouble and only then did they start developing felling for each other and how even now no one is allowed to question Zaryusu placement in the relationship less they incur the wrath of those two . Zaryusu on the other hand is living his best Bi dreams) .
Then we have the thieves , and it goes like cannon . Until the Empire and specifically Jircniv has to answer for his messes . Naturally he is scheming on who the master of the tomb is and how to make things in his favor or at least mitigate as much damage as possible . Then he meets Momo in the throne room with all the guardians and is met with the smell of multiple Omegas and Alphas ( who are lowkey terrifying in that none of them seem to be very active in the bedroom in anyway , which considering one of them is a an actual succubus means that either their master forbids them from indulging in pleasure or they are are doing this voluntarily . Because while 1 or 2 of them being ace is unlikely but possible , however if it's all of them then it smells of foul play on someone's part . And he is right , only Pandora Actor is genuinely a full aroace , Cocutus is more interested in practicing his swordsmanship and learning how to rule the lizardmen to even think of making babies as of yet , Sebas is a demi in both romance and else and is currently building the foundation for everting else with Tsuare not to mention his dragon paced metabolism significantly lowers whatever libido he might have had , Ainz is an undead , stressed and more preoccupied with not getting caught lacking and then Albedo who is the only non-Beta person in Nazarick that wants to get laid except she only wants that to happen with the stressed skeleton . No one is getting any sex whatsoever .) . Then when Momo came closer Jircniv finally understood how fucked he was , as the master of the tomb is an Omega , a terafyingly strong Omega . And so immediately his plans go head first out the window because 1) that is a undead so sex isnt gonna entice him 2) That is an Omega , women aren't as enticing for him as an Alpha would be and 3) he made someone break into an Omega’s territory and maybe even nest . If there is anyone , even one person , being or even object that Ainz Ooal Gown considers as pack they are all going to suffer for putting it at risk to . Thankfully no one died , but that was only the start of the terror and headaches that will become Jicniv norm . The Cacce plane is a horrifying nightmare that will haunt everyone other than its perpetrator and his direct subordinates . Gazef also died , even if it all feels as an after thought after everything that happened that day . Jircniv is reasonably terrified as is everyone , but he is especially terrified as he starts to receive courting gifts from Ainz and his Alpha is for some reason unreasonably delighted and keeps urging Jircniv to send his own gifts to the very Omega that makes him slowly go insane with paranoia . As Jircnov starts to slowly but surely become acquainted with everything that an Omega noble deals with when a more powerful Alpha noble puts their eyes on them . Because even though he is an Alpha and Ainz is an Omega , it is for sure him that feels like a cornered lamb trembling in waiting for the hungry wolf to finally show his fangs and for the pain to start . All the while he is also suffering from unpredictable and almost constant ruts happening as his stress levels only continue to rise and rise (Ruts and heats aren't actually for reproductive purpose but rather just the body trying to relieve stress after a certain point , it's just that they gained the reputation because most people chose the fastest and least bloody method to relieve stress aka sex rather than say nest for days or go fight someone) .
Eventually the boredom of ruling kicks in so Ainz decides to go fight in a collusion and even heard that Jircniv keeps with the happening in it so while he might not witness him fighting (proving himself as a strong , reliable and worthy mate) with his own eyes he would at least heard of it after it happens . And of course to make things interesting he agrees on the no magic rule . Imagine his delight at Jircniv being present to watch him fight (the misunderstanding with the church is even worse now as they don't just think he is betraying humanity but betraying it to have sex with the undead(they are judging him and giving him the side eye so hard even as he is trying explain he had no idea of this happening while his Alpha is delighted to see Ainz)) . Internally Jircniv is having the battle of a lifetime , as his logical and human side are panicking as to what the demigod Omega is going to do to them while trying to think of ways to keep humanity alive all the while said logical and human side are trying desperately to stop the Alpha side of him from immediately throwing himself in the arms of said undead and starts rubbing his pheromons(made from mana) in his bones to make everyone else back off this amazing , strong and smart Omega that has shown interest in him humanity be dammed . Eventually the two sides come to a cease fire and Jircniv request the empire become a vassal state and to marry him(ainz is similarly to cannon shocked but wants it in writing) . The champion is also like everyone in this au even more terrified of Ainz than in cannon , specifically in this situation he hopes that even if he wins he doesn't immediately die after (because with the Emperor just proposing if his opponent dies his head will be rolling not too long after ) . Eventually he loses , dies , is revived and quickly gets out the coliseum because he doesn't want to be between the strange romantic/erotic/courting tension the two monarchs are having with each other and not a small portion of people in the stands agree with him on that . Especially since the emperor look like both the luckiest man alive (The Omega he just proposed to more than thoroughly showed his combat and strategy skills making his sapiosexual self and Alpha very very happy) and the most miserable man on the world(his logic and human parts are in a total state of panic from the goddammed demigod of an undead Omega and his Alpha is sulking from not having his proposal immediately accepted) .
Not to worry however as not even a week later both proposals get accepted and they do the wedding rather quickly . And for a honeymoon they go to the dwarfs (and that is how we have the Dwarfs Arc) and establish new trade routes while being away from documents and sightseeing the mountain . While that was happening Jircniv is slowly getting seduced by Ainz(unknowingly on his part) by being competent and caring (Jircniv is definitely coming up with theories on Ainz somehow knowing every little part of his taste and creating a way to hit all his weak point and get him madly in love ) . Because he is kind and parental (parenting Shaltear and Aura) , ruthless and efficient (conquering the dragons and Klagoa) , a diplomatic mastermind (convinced the dwrafs to not only trade with him but also made the runesmiths follow him into his country less than a month after meeting them while being an undead) , knowledgeable about his resources and how much he is willing to spend on projects (the Klagoa) and unquestionable military and personal might (the dragons) . And he is doing all this hard work on the honeymoon while still making time for Jircniv and spoiling him (the dwarfs couldn't exactly tell if a few tings had gone missing after they caught Jircniv’s eye and Momonga noticed or if they caught Momo’s eye by reminding him of said husband , and it's not like Gondo is gonna tattle on his new monarchs especially after he also got 1 or 2 small things with runes as bribes not to mention that he does genuinely like them or at least Ainz enough he is willing to keep silent on a few things going missing) . And sure technically the honeymoon could have been bigger or grander but it got them free of work , let them slightly loot a palace , establish a new trade agreement and getting raw material for a few things one of which ended up being a new accessory for Jircniv from the scales of the frost dragon Ainz killed . It was fruitful and it had the nice bonus of getting Jircniv very acquainted with Ainz’s ability to provide him with what he wants all on himself even when not counting his vast fortune or extremely skilled subordinates/children . Also Nazarick has all the luxury his heart could desire so that was genuinely a break of scenery . Eventually he also learns that not only is Ainz the defacto only present parent figure in the tomb but that the world those children come from and the world he himself comes from are both ones with no secondary gender (which explains a lot , especially the fact that apparently Momonga has been flirting with him unconsciously on his part and that the only reason he didn't get his smashed to pure when they first met being that Ainz Omega side took a very very strong liking to him with Momo not knowing that his Omega instincts were suggesting kidnapping him not letting him go with only minor problems) . Eventually he too get put in Nazarick’s short list of parental figures , and sure it's a little strange to be parenting so many fully grown people for both his logic side and inner Alpha but it makes Ainz very happy his pack and mate get along so well he is even extra cuddly whenever possible or whenever the one of his rare heats hit him and he gets in the nest with Jircniv and 1 or more NPCs and starts cuddling them .
The Re-este are overall is in a shit position ever since they lost the kingdom’s strongest aka Gazef and they cant even use political marriage(with the very valuable political pawn(hahah) that is princess Rener (who presented as an Omega) to solve the problem because 1) Ainz Ooal Gown is an undead 2) He already has a beyond beautiful Omega subordinate 3) He is an Omega so Rener isn't as appealing as she would otherwise be and finally 4) He is still newly wed to the Baharut Emperor who is an Alpha . So sending Rener in would almost certainly equate to making things even worse . Just because the undead might not have the reproduction part doesn't mean they don't have the rest of the package of instincts and they might even have it stronger , so anyone trying to take away their mate , children or nest is going to go down fast and hard with no mercy . So sending a beautiful (for their race) Omega of the same race as his Alpha will almost certainly be interpreted as a declaration of war .
Then the Holy Kingdom arc comes in . Calca still dies , Ramidios is still massively racist (Jircniv is definitely with Demiurge and Albedo planing he death to be as painful as possible) , Neya still gets her religious awakening (along with presenting as an Alpha but still being a lesbian disaster and with Ainz unconsciously parenting her) and the Demi-Human tribes are still united under Momonga’s banner (Every tribe has their gender norms and while he reaffirms those of some for others he fully breaks them) .
Then Filiph and his idiocy happens . And his overinflated ego thinks that not only is he going to get Albedo but that Ainz did all of this because he wants to be his mate and is using the Bahamut Emperor as a place holder as they kinda look alike . And Philip in his “generosity” of a “proper Alpha” is willing to take Ainz as his main wife and make Albedo a concubine of his while becoming the Monarch of the new country his soon to be mate made (Philip is delusional as always) . Or if in his military brilliance he conquers the Sorcerer Kingdom and his given princess Rener as a wife he still doesn't mind taking Albedo and Ainz as his concubines (as stated before power is very attractive) . Jircniv was very happy to hear that Nuronist and Pestonia have teamed up to make him regret ever being born after Ilma reported his delusions to him and Albedo .
The dark elves would like to say that they are very very jealous of the lucky Alpha that is Mare’s and Aura’s uncle’s mate . The elf king is getting absolutely tortured to death after what he said to Momonga’s kids . And Zeshi is currently praying to the wrong gods to “please come get her she is scared” (should have been praying to Ainz Ooal Gown then he might have lessened things) .
Platinum is lowkey terrified as is everyone else because the last time an Omega this powerful was in the world many species started going extinct and the dragon almost did too .
