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“You know,” Isabelle tells him one night, standing on the front steps to the Institute so that she’s looking Alec in the eye, “I can look after myself.”

On paper, Alec knows this.


Isabelle is the dictionary definition of can look after herself . People back away from her on the subway. She’s stopped several muggings by just giving the attacker a harsh look, and they weren’t even aiming for her, anyway, because, again - Isabelle is terrifying. She’s been terrifying ever since she was twelve and got that damned whip as a birthday present, since she was thirteen and learned to slit a man’s throat with the flick of her wrist, since she was fourteen and getting drunk in Alicante with her eyes bright and her mouth twisted into a sneer. She’s been terrifying from the moment she realised she would be beautiful one day. The memory of the small, devoted toddler who used to follow Alec around everywhere is long gone, replaced by a woman capable of breaking your neck in five different places in as many seconds.


Alec’s not his sister’s keeper. Isabelle wouldn’t let him be, anyway. 


“I know,” Alec says, scratches the freshly-healed cut on his arm. Isabelle leans over to bat his hand away, and when she does, the ferocity of her gaze softens. 

“Just checking,” she says at last, and goes inside without looking back.


Isabelle is Alec’s responsibility. His parents tell him as much every time they go off to Idris, or Europe, or wherever their role as head of the New York Conclave takes them: look after your sister. Make sure she doesn’t get into trouble. If they knew Isabelle a little better, they’d know that into trouble is Isabelle’s default state of being. If they knew Alec a little better, they’d know they didn’t need to ask.



When his sister turns eighteen, Alec stays at the Institute overnight. Isabelle sneaks into his old room and bursts into hysterics.

“Eighteen was always your age,” she sniffs, her eyes red-rimmed in the dark. Her hair is down and falling over her shoulders like a sheet of silk, and she looks five years younger than she usually does. Which isn’t to say she looks thirteen, either. Isabelle’s been pretending to be an adult long before she ever became one. “And sixteen was mine. I didn’t think-”

She cuts herself off before she can say it, before Isabelle can commit the grievous sin that is vulnerability in the Lightwood household. “It’s not like I wanted to die,” she continues after a pause, when she’s got a hold of herself and is no longer dripping tears all over the comforter. Alec pets her hair gently, the way he did when they were children. “I just didn’t think I was going to live, either.”
Alec knows the feeling. He knows the feeling so well that his hand stills in his sister’s hair, and he thinks he’s going to be sick.

Shadowhunters die young. That’s always been the excuse presented to them, Alec thinks, whenever someone at a Council meeting protests the high mortality rate of teenage trainees. He wants to say that sixteen is more than just young . At sixteen, Isabelle hadn’t even lost all of her baby fat; at eighteen, her face is still soft and rounded in the places where their mother’s face has hollowed with age. 


Sixteen is old compared to, say, nine, but that’s about the only time it ever could be.


“Happy birthday,” Alec whispers when the Institute clock chimes two o’clock in the morning. Isabelle was born early - born impatient, born ready to grow up before she was supposed to. He has the fuzziest, vaguest memory of his sister at six months old, desperate to walk before she could crawl. Eighteen-year-old Isabelle wipes her eyes on the hem of her sleep shirt, and pads back to her own room.



He’s expecting a lecture from Magnus when he gets back late. Something about how Isabelle doesn’t need him to accompany her on patrols as an adult, or a snide remark about the fact that, even when they're both grown, Alec still works himself up about her sneaking out to go to Downworld ragers. At fifteen, his concern for his little sister was understandable; at twenty, it’s overbearing. That’s what his parents think, even if they won’t say it. Even if they spent a lifetime telling Alec to look out for her, and it’s the one order of theirs that Alec never hesitated in following.


Magnus doesn’t give the lecture. He doesn’t even make the snide remark. Instead, he slides a mugful of tea over the counter to him, and says, “She’s lucky to have you as a brother, you know.”
“I doubt she sees it that way,” Alec says. Isabelle used to chafe under the weight of Alec’s protection when she was a kid; her ego must be beyond blistered at this point. He’ll have to let her go, eventually. Alec knows he can’t follow her round on patrols forever, as much as he wishes he could. (He left her alone with Sebastian, and see how that turned out?) But the thing is, he’s so used to looking out for her that the thought of not doing so feels like a betrayal. “You know, when we were little, she used to cry because she thought I wasn’t hitting her hard enough when we sparred. Then she figured out that crying was a waste of time, and started to redirect all that rage into training with every deadly weapon she could instead.”


That’s another thing Isabelle was born as: angry. He can’t remember a time when she wasn’t.

“Why do you think you still carry all that round with you, Alec?” Magnus asks, gentle. Like Alec doesn’t have the weight of Isabelle throwing away her adolescence for him on his shoulders, the heaviness of her own self-imposed sacrifice crushing on a good day. As if the first time Isabelle ever scared him , she wasn’t thirteen and pretending to be older and pretending to be the one thing even more unacceptable than Alec’s entire being .


Alec shrugs. “Someone has to.”


Because, and here’s a secret that Alec will never tell: sometimes he thinks that if he doesn’t remember Isabelle as a child, as a wide-eyed, vulnerable kid and not the killing machine painted in red lipstick and black eyeliner that she has become, then nobody will.


When Isabelle’s nineteen and tying a tourniquet round the poison-infected demon bite on her leg, it’s not Jace she calls, or Clary, even though they’re both at least a block closer to her than Alec is. Instead, her voice is tinny when Alec answers the phone and she says, “Alec? Can you come pick me up?”

Isabelle can look after herself, Alec knows. If he tells her no, that he’s on his way to meet Maia for an emergency Alliance meeting, she’ll find an alternative solution. That’s just what Isabelle does. She’ll get Jace to haul her through the streets of Manhattan while she gripes and groans instead.


Alec doesn’t say no. Instead, he reaches for his weapons belt and shucks off his denim jacket in lieu of fitting himself out in gear. “Of course,” he tells her. “I’m on my way.”