PREFACE
(Wow, I feel like it's been a while since I've done one of these...)
This is an AN chapter! Story begins in the next chapter. (Posting M/W/F for the next four weeks or so.)
So, this story actually takes place in the canon timeline of book 7, which is invaded by an OC (who does not have time for any of this shite) and then by aliens (which is the reason there is no time for this shite). For context, we have a short summary of the major events of the last few years of the war in the alternate timeline the OC comes from, and for anyone who's curious, there are a few scenes showing exactly how Mira ended up where she did in a separate story called "The Princess in the Tower". If you'd like to skip straight to the story (So There's An Alien Invasion On, NBD), feel free to do so. Anything that's really important to the narrative will be covered again in-text.
Mira Black is from an alternate timeline wherein:
James asks Lily to the last Hogsmeade weekend of their seventh year. Unlike in canon, she says no. James didn't really expect her to say yes, and asks Tiffany Davis, a Hufflepuff 6th year, instead.
In much the same way that Lily and James's relationship (in my headcanon) would have developed largely as stress relief, Lily and Sirius develop a relationship, based largely on bitching about how badly Dumbledore is handling the war and being the only dark-minded people on the side of the Light. James, who is happy with Tiffany, gives Sirius his blessing, leaving his infatuation with Lily firmly in the past. Sirius hates Tiffany with a burning passion. Lily thinks this is hilarious.
(You know he's going to have to marry someone eventually, right? A female someone who will have little Potter babies for him. — Yes, but I don't like this one! She's just so...Hufflepuff-ish! Sweet, and just— It's sickening, Evans, it really is...)
He eventually realises that most of the reason he always hated Lily so much was probably jealousy, because they actually get along better with each other than practically anyone else.
Lily still twists Tom's ritual into a tynged in September of 1978. She and Sirius start shagging relatively soon after. James proposes to Tiffany in April of 1979, after the Glastonbury battle where he almost died. They're married in June. Their eldest son, Henry, is conceived on their wedding night. James and Tiffany move to Godric's Hollow, Remus goes to spy on the werewolves, Sirius moves to a property called the Folly (left to him by his blood traitor uncle) and invites Lily to move in with him.
Siri intercepts a letter from Bella to Lily in October of 1979, trying to convince her to undo the curse. Sirius takes this much more seriously than Lily, because he knows Bella wouldn't ask for help unless this was serious. Lily reaches out to Sev to find out what effect this tynged is actually having; Sev confirms that yes, the Dark Lord is going insane, that's a large part of why things are escalating recently. Siri reaches out to Zee to arrange a parley with Bella.
At the parely, only a couple of days before Samhain, Lily agrees to remove the tynged in exchange for de-escalating the war. Bella removes the sterilisation curse she put on Siri when he was like fourteen because Reggie is dead now, which means Sirius is the last hope for the House of Black. She of course doesn't tell him.
The Diagon Alley Massacre still happens on Samhain of 1979, because plans were already in motion, and Tom overruled Bella's attempts to call off their attack. Lily still animates the dead. Lily and Sirius's eldest kid, Mira, is conceived in the aftermath, because fuck, Evans, that was hot...
They plan to reverse the tynged at Yule. Bella manages to temporarily enforce sanity on Tom through their soul-bond, long enough to explain about Lily and the tynged, and convince him to help reverse it. (Which he has to, because he helped cast it.) Lily appeals to Hecate to release the curse; Hecate mentions that Lily is Tom's daughter, in front of Tom, Bella, and Sirius.
Lily sort of wants to defect to the Death Eaters, if they're not going to be completely insane, but they're not going to drop the war entirely, just go back to raids and defending themselves against Crouch like they did when the Marauders were in school, and just the raids are bad enough. Sirius 1000% has not made things up with Bella and/or the House of Black, even if Bella sort of acts like he has, randomly coming over to have tea and get to know her "step-daughter" and inviting them to the Festa Morgana and shite. He still thinks the House is rotten to the core and Bella is fucking insane, which are both completely accurate assessments. (Lily actually thinks Bella is fun and interesting to talk to, as long as they completely avoid the subject of the war.) And they need to stick with the Order to try to convince Dumbledore to de-escalate as well. Unfortunately, they don't exactly have an in with Crouch to make him back off, and he takes the Death Eaters' lack of big retaliatory battles as an indication that he's winning, so he keeps pushing.
Lily realises that she's pregnant in January of 1980. She tries to fix that ASAP, but Sirius catches her and talks her out of it. They tell a few close friends.
Lily and Sirius reversing course on the issue of escalating their own tactics to keep pace with the DEs raises suspicions, especially with Sirius's familial connections and Lily blatantly using Black Arts on Samhain. Pete, up to his ears and sinking fast in this whole spy thing, mentions that Lily's pregnant with Sirius's kid to his handler, who passes it up the chain to Bella. Bella is delighted, because A, her favourite cousin is having a kid to carry on the Black name and legacy and B, Tom's daughter (basically her step-daughter) is having a kid, and she doesn't have any aunts or older sisters to tell her what to expect, so clearly this is an excellent excuse for Bella to be nosey.
Henry Potter is born in late March of 1980. Sirius is named as his godfather.
Tom makes a point of re-focusing his rhetoric on independence and magical freedom, as opposed to the magical/pureblood superiority angle that his recruiters have been pushing at Hogwarts (which is appealing to a certain segment of spoilt noble brats, but really no foundation for a movement) and expanding his messaging to the commoners in general, as Crouch becomes more and more draconian, trying to ferret them out. (Arresting people who have nothing to do with the movement and questioning them about any potential Death Eater sympathies they might have, etc.)
Bella convinces Lily that she and Sirius should get married, because Siri might be disinherited, but his children aren't, and while the Blacks do recognise bastards much more often than most noble houses, his kid will have more legitimacy if they're actually legally married when it's born. Lily, who is much more sold on this whole House of Black thing than Sirius at this point, convinces Sirius to do it. There aren't really any good holidays left before the kid is likely to be born (Midsummer, but that's traditionally when Light Houses do their marriages), and Sirius is less than entirely comfortable about tying himself down (their relationship has been very casual, really), so they do it on Walpurgis (May 1980), which is the absolute worst time of year to make a binding commitment, in a year-and-a-day type deal. Basically just to legitimise the kid.
In June, Malfoy suggests that Sev apply to be a Potions Master at Hogwarts and also a spy/glorified messenger boy.
Lily and Sirius's kid (Mira Calytrix = Mimi) is born at the Folly on Lammas (31 July 1980), with Pandora and Bella as attendants. Bella sticks around to help out for a while after Pandora goes home, because the one part of being basically nobility Lily isn't comfortable with is the elves because servants sort of freak her out. The Black Family Magic makes an appearance to poke at the baby and ask if this is the new heir. Bella offers a "benediction" — passing on a copy of the magical symbiote thing and just sort of...touching up a bit around the edges, making the kid a little quicker and smarter and more graceful, giving her a better sense of timing, etc. You know, basic fairy godmother shite. Sirius shows up at some point in the middle.
(Pandora told me I could come ba— Lily, why is Bella giving soulfire to our baby? — Why, shouldn't she? — Er. Well...I don't think it will hurt her, but it's just...really weird? — ...is Bella ever not "really weird", Sirius?)
Jamie and Sev are named as Mira's godfathers.
Tom offers to negotiate peace terms again on Lammas, which Crouch refuses. In retaliation, the Death Eaters attack King's Cross (31 August 1980) and begin making plans to simply take the Isle of Man and hold it indefinitely.
Snape begins teaching in September, nominally as a spy, but Dumbledore knows he's a spy, and Tom knows that Dumbledore knows, so Sev is mostly just a glorified messenger boy.
Samhain of 1980, Lily and Sirius (who may think it's weird to ask Death to bless an infant, but is far more on board with it than James would have been) present Mimi to Persephone.
Yule of 1980 marks the beginning of the Death Eater occupation of Mann. New Avalon is founded, and fuck the police. Peter takes this info to Dumbledore when he finds out, but he's too late to stop them. Dumbledore orders Peter to continue spying for the Order within the Death Eaters.
In January of 1981, Crouch attempts to use Bella's tactics to draw the Death Eaters out by staging raids on the Starlighters. Bella assassinates him, because that's just not cricket, especially when the Death Eaters had already withdrawn and were fighting a purely defensive war on Mann.
(You mean you could've just killed him at any point? — Well...yes? — Damn it, Bellatrix...)
Lily and Sirius argue that the Light should just let it go, Crouch deserved it for pulling that shite.
(Oh, and Bellatrix doesn't? — Bellatrix has kept up her end of the deal, scaling shite back. At this point it's the Light that's really pushing this conflict. — They're occupying Mann! And what deal...? — Er. The one where I un-cursed de Mort in exchange for them de-escalating? It was a win-win, really, since I'm pretty sure things would've gone a lot worse if he became the parody of himself you all talk about him as... And so what? They're not hurting anyone on Mann...)
Peter discovers that Lily is Tom's daughter. He begins investigating her activities more closely and realises there's a disturbing pattern of behaviour with her defending the occupation of Mann and un-cursing the Dark Lord.
(Are we really sure she's on our side?)
He talks to Sirius, who assures him that yes, of course Evans is on our side. But this is the same Sirius who fucking hated this girl all through school, and it's sort of suspicious that they're married now, are we sure there wasn't a love potion involved? Pete gets paranoid and tells Dumbledore everything.
Dumbledore questions Pandora about Lily's ritual activities, pressuring her with "subtle" threats to reveal her own ritual healing practices to the authorities. She admits that she saw Lily channel the Dark once (almost two years ago, by this point), that Lily is in regular correspondence with Miskatonites, that Bellatrix was present at Mimi's birth, and that she knows Lily introduced Mimi to Death last Samhain. This, along with the public ritual magic he's already aware of, paints a very disturbing picture of a young woman falling to the Dark and dragging her husband (and probably her infant daughter, too) down with her.
Dumbledore goes to the Folly to confront Lily and try to talk sense into her. This goes predictably terribly, especially when she says if she's not welcome in Daylight society anymore, she'll take her husband and child and go join the Dark, then, because she always did like their politics better anyway.
(I'm afraid I cannot let you do that, Miss Evans.)
Dumbledore moves to take her into custody, like he thinks Sirius is going to sit there and let him assault the mother of his child. They get into a massive fight. Sirius has Dumbledore on the ropes (Dumbledore is more powerful, but Sirius is much better trained and his family is on the line here, so he's more desperate) when Order/Auror reinforcements arrive and capture both him and Lily.
Lily is sentenced to be thrown through the Veil at midsummer of 1981 for practising black magic; Sirius is sentenced to life in Azkaban for using the imperius on Dumbledore in their duel (as a shield-breaker and then to force him to stop fighting...right before the Aurors showed up, so that was just great...)
James is fucking heartbroken because how could he have been so wrong about Sirius and Lily? But he agrees to take custody of Mimi and raise her properly, in the Light. This goes well...until he realises that not only is she a tiny creepy mind mage, but also her imaginary friends are actually gods. He hands her over to Dumbledore, who keeps her mostly isolated at Hogwarts until the summer after what should be her first year, when she escapes with the (largely unnecessary) help of Henry Potter and a couple of his friends.
She moves to New Avalon for a few years, then decides that she wants to take a position as a Junior Librarian/Diplomatic Envoy to Miskatonic, which is why she's in the Americas when the alien invasion begins, in the autumn of 1997.