Mia is first to notice.
Tonks' glances are surprisingly furtive, considering how much attention Tonks brings to herself; her clothes, her hair, her laugh, her conversation... her ability to trip over even floor surfaces.
Mia supposes that Tonks must have been somewhat furtive to get into the Auror Corpse, but figured, like everyone else, that it was her amazing metamorphic abilities and probably her spell work. Silly really, because that's probably what Tonks wants everyone to think, the image she probably painstakingly cultivated.
It her quick glances around the room, lingering not quite on a few people – just over their shoulders or above their heads – but definitely lingering on Remus (it's the way her eyes focus, you see).
It is also in her seating arrangements; she usually sits diagonally opposite, usually down a few seats, so that she can see him from the corner of her eye as someone speaks at the head of the table.
That she's managed to bollocks up everyone else's drink, aside from his, and that he's the only one she hasn't yet spilt food on.
Sirius notices the self deprecating smile on Mia's lips and flicks a knut at her.
Mia laughs and says she just noticed that she and Tonks do have something in common after all.
Sirius is confused.
The reason Mia is the first to notice? Because she acts the same way around Sirius.
She never sits directly opposite him, always to his left so she can pretend to be watching the speaker when she's actually admiringly something about him – his hair, his lips, his hands...
She doesn't actually need an excuse to furtively glance at him during the day because they're usually in conversation, and it's rude not to look at someone when they're talking to you.
She can make his drinks and favourite food (fish-finger, mustard and olive sandwiches) perfectly when she constantly has to ask Remus how he has his tea even though he has it exactly the same as she does.
So when Dumbledore damns the person killing off the death eaters Mia isn't at all surprised that Tonks looks grimly satisfied.
She is surprised that later when it's just she, Remus, Sirius and Tonks in the library at eleven that evening, that Tonks looks to her and asks how she can help.
Tonks isn't surprised that Mia assigns her to Pettigrew watch.
Tonks has seen the way she looks at her cousin, exactly like the way she looks at Remus. She knows that Mia is after Pettigrew simply so Sirius can be free to walk down the street with Harry, can be free to look after his godson like he should be able to.
It's the same sort of reason she's slaving over the Wolfsbane recipe, experimenting with toxic ingredients, potentially poisoning herself every time she drinks some.
Remus should be free to work anywhere he desires, to walk down the street un-harassed, and to finally look up at a full moon free from fur and hunger and violence.
"It's why we can't ever admit it out loud."
And then it changes.
Remus changes... his seat.
Usually he sits four seats down from the head of the table, where he has a clear view of the speakers face, and enough room to keep notes.
Today he comes in a little later than usual and sits eight seats down – further down the table than Tonks. His notes are somehow not quite their usual detailed selves, though it is hard to pin down exactly how they are different.
He doesn't go back to his usual seat after that day.
Mia catches a peculiar look on his face one day in the library.
It's a mix of shock and longing, she decides after ten full seconds of studying the foreign mix.
When Tonks picks herself up from the floor, with the pile of books she dropped, Mia sighs sadly, knowing that eventually they would happen.
Sirius finally catches onto Tonks, though he admits, it's because he got her drunk and managed to find out she fancied someone from the Order through a game of twenty questions. From there, he says, it was a process of elimination: not her own cousin, not anyone over sixty, and no-one could love Mad-Eye.
Mia points to Severus and Sirius turns a fetching shade of green, and after a quick confirmation via a paper aeroplane (EW that is gross! I do not fancy Snape, you idiot!) Sirius once again reasserts that Tonks definitely fancies Mooney.
The evil grin makes everyone who looks his way edge away in alarm.
Sirius comes crowing into the library not three days later, shattering her eardrum as he delights in telling her that last night he got Remus famously drunk and that the man admitted he'd been *mooning* over Tonks for a while, before throwing up everything he'd eaten that day and passing out slumped in his chair.
Mia rubs her temples tiredly.
Sirius meanwhile chatters excitedly about all the ways he could become a matchmaker, and then he'd get to give the pair of them the 'you'd better treat him/her right or I'll smash your face in' talk like the good cousin/blood brother he is.
Mia groans but secretly thanks the unlikely pair; Sirius hasn't looked so mischievous in months.
She is surprised into statue-like stillness when Sirius proposes at Christmas.
Judging by the smug expressions on Harry and Tonks' face they knew something was up. Remus is surprised but more because Sirius could keep something like that a secret. Mostly he is jealous which he tries damn hard to hide.
She desperately wishes to scream yes but the practicalities of a vampire/human relationship rear up into the forefront of her mind. Mostly her reservation comes in the form of 'I do not wish to die, but I would not know how to live on without him if he does not become a vampire'.
But his eyes are beseeching, wiling her to say yes, and something flickers under the surface that somehow she knows means he has thought it through, if only she would trust him enough to say yes.
If Mia trusts anyone enough to follow blindly it is Sirius.
A faint YES escapes almost unconsciously, but he hears it and his face lights up like a million sunrises blended together before he pounces on her, lifting and twirling her in joy.
Their lips meet for the first time and Mia finds her soul.
A year later when Tonks is thrown down the steps in the Ministry in the Death Eater attack Remus finally realises where his soul lies and by the time the Auror wakes he has purchased a ring.