The room is cold, gray, the young boy standing stiffly in the middle a stark contrast.
He is the only warm thing in the room, and Alec shivers and he approaches him.
A warmth fills Alec's chest as he sees the nephilim relax from the stiff pose he'd been in before as he sees Alec. He remembers flashes.
Flashes of Jace reciting the vows, drawing the rune on Jace, the first and last time he'd actually draw the Parabatai rune, the searing pain as something rips away from him as Jace completes his own.
It is agony, his soul slips away from him, as he clings to Jace, his shaking hands gripping his brother. And there are hands on his arm, clutching him just as hard, in a death grip.
He feels the pain lessen, his body numbing in its wake. His grip loosens and he feels himself tipping over into Jace.
The last thing he'd seen before he dies is the Parabatai rune, the black standing out starkly against too-pale skin.
Most people didn't understand the depth of the Parabatai bond, most come out malformed, and stunted, like in his father. It is not an exchange of a part of one's soul, but more— a congealing of both souls into one. He and Jace shared one soul, not two, the lines between the two blurring until they were AlecandJace and not two people at all as they recovered from the ceremony.
Alec thinks that theirs is as perfect as it is because he was barely a person before the ceremony, but that's okay—great— because Jace certainly was and Alec had enough sense of responsibility to balance his wild, bright, bright, bright soul out. And the soul they share now? It's whole, it's one, not like two new ones connected. It's what a Parabatai bond should be. His parents are proud, but also alienated, and scared. This is too close. The bond too perfect. They fight as one, accidentally complete each others sentences. Alec doesn't care much because now he has Jace to himself forever and Izzy's not running.
They get a shared room now, with a divide, because they're one soul but separate people. They love it, because they don't have to sneak into each other's rooms anymore and Alec's side of the room is too littered with their stuff to ever enter, let alone sleep in. Jace figures out that even if they learn only half the books themselves, they can just get the rest of the information from each other. Alec agrees, but learns anything important twice over, sending knowledge to Jace just in case he isn't there someday. He's not as good as his parabatai, and he's probably going to die first, probably on one of Jace's harebrained schemes. But it's good, it's better than good, because it's easier now when Alec wakes up in the middle of the night to check on his family. Now he can feel Jace as soon as he jerks awake and the hallways don't seem quite as cold anymore as his Parabatai accompanies him, teasing, but never judging as they go so that Alec can calm down as he hears their sister's steady breathing and, occasionally, break in and sneak under her blankets. He doesn't complain even once, even when it gets really bad, and nor does his sister. They get better, training with Jace is different with their bond blown open, and Alec doesn't only improve his balance, but also Jace's as Jace does his.
Then they're older, and Alec doesn't have eyes for anyone else and Jace never sleeps with the same girl twice and he comes back to Alec every night after the missions are over. They fight better now, the strain of processing twice as many attacks, defenses, is barely noticeable with the strength of the runes drawn by Jace's hand they fight as one, four blades, not two and two. He's aware they look emotionally constipated, but there are no secrets between them. Can't be. He glares at the idiot redhead in the day and holds his Parabatai in the night as he tells Alec, in mumbles incoherent to anyone else, about her. They fight, but people only see the surface of it, and most words unheard by all but them. The reassurances, the this is a bad idea, and the you know I'm the one who'll get killed, because I can't let you die. Alec likes her the way Jace does, not by himself, but by extension. But she doesn't seem to realize how great his Parabatai is, and so he is cold. The mundane is amusing but annoying, Alec thinks he would've liked him in other circumstances, when things had not gone to shit. And so he summons and fights demons and Circle members and rolls his eyes at his Parabatai's expression as he hears Alec's thoughts about the most stunning man Alec has ever seen. (He senses Jace's approval though, a kind of I'm okay if you're okay with loving him.)
He's staring at Magnus, unstyled dark hair framing his face, unable to sleep without Jace. And then he's sitting up, screaming as Valentine touches Jace and they're hurt 'and this shouldn't be happening— He needs to save— they hurt and— he sees a glimpse of blue magic before he passes out. When he wakes up, Jace's beside him, and they're in the medical wing of the Institute. Magnus had tracked Jace through him, and by the angels, how did he not think of that before? There are tear tracks drying on his face and he has flashes of memories, Jace staring down at Valentine, Alec, curled up, saying Jace's names again and again till it becomes a blur, of Izzy, Simon, and Clary rescuing him— Jace, technically— from Valentine. Jace isn't in pain anymore and Alec checks him for wounds before curling up and falling asleep again.
When Magnus asks him to move in the first time he says no, because how can he tell him that there's a reason that Parabatai are assigned to the same institute, and they marry different people but still stay together? He doesn't know if Magnus is okay with the bond in the first place, and Magnus doesn't know that he's a package deal yet. He's hoping to keep it this way for as long as he can before Magnus leaves him, and the world burns and falls apart, both inside and outside of Alec.
They manage to keep the world together and he sends Jace waves of calm as Clary leaves Jace, and then immediately moves halfway across the world.
Jace is the one to explain it to Magnus, in the end. The next day, Magnus asks both of them to move in, and they kiss him, first with Jace's mouth, then Alec's but there isn't a difference, not to them, and by the lack of surprise and light in Magnus' eyes, he knows that he's beginning to realize it too. Then Alec glances as Jace through his own eyes and realizes that half his eyes are the dark blue of his own instead of their usual gold, and feels like an idiot. Of course Magnus had realized. They glamor when it usually happens, which means nearly all day, but in Magnus' loft, they don't bother. Magnus pulls them close and they fall in love with Magnus all over again and Jace gently pushes Magnus onto their bed, Alec falling simultaneously, in sync, because Magnus' not the only one Jace's pushing, and sometimes he's just another body of Jace's just like his Parabatai's his. Alec tries to suppress a laugh when Magnus' glamor falls and Jace repeats, "They're beautiful, Magnus. You're beautiful."
"You're the same person," Magnus laughs. "How did I not realize it before?"
But they're not, not quite, because they're different in execution, Jace killing everything bad to protect people while Alec tries only to save, not fight. Alec has stared at Magnus while saying the words, Jace says them mostly into Magnus' mouth, barely pulling himself far enough away to see them. He doesn't need to though, not when Alec's looking.
Jace has always known and Magnus has long since figured out that Alec's not good at intimacy and the first time Magnus catches Jace in his underpants in front of him, it's not in bed but with melting shoes and a pink shirt, a hilariously oversized sword in his hand. It immediately turns into a flail and the other end falls, cracking the floor of the training room. Alec, on the other size of the room, is laughing so hard that he's about to fall and Magnus looks enraptured. It appears that he isn't the only one who's fond of Jace's ridiculousness.