Pairing : Malec
Trope(s) : A/B/O verse, Parabatai Bonding
Trigger(s) : Infertility, forced body modification
Mildly NSFW - in line with A/B/O stories
Long-ish - full info under the cut!
Following general canon timelines - Alec is an omega who uses scent blockers to appear as a beta. Magnus is an alpha and they start dating as per canon.
Alec tells him early on that he's an omega - Shadowhunters are the ones with an issue with it, not Downworlders. When things start getting steamy, Alec keeps pulling away. Magnus is his usual sweet and awesome self and waits until Alec is ready or wants to talk.
Soon enough Alec goes into heat. Jace always sticks them out with him and this time he calls Magnus asking him to come over because Alec wants him there. Magnus knows the uncontrollable alpha ideal is just an excuse for them to act like monsters and knows he can be near an omega in heat just fine and agrees to go.
Turns out Alec is in horrific pain and there is definitely nothing sexy about it. His smell is tainted with fear and pain. Magnus takes care of him and cuddles him, while Jace stays close by to watch over his Parabatai.
Once it's all over and Alec has rested up, they talk about it. When he was a baby, they tested him for his second gender and when Valentine found out he was an omega, he had all of his reproductive organs removed either as punishment or as a way to 'remove' his omega status - who knows what evil thinks. (How much Robert and Maryse knew / approved is up to you.) It left him with pain in his abdomen; it gets borderline unbearable during his heat and starts up when he's 'in the mood', which is why he can't go further with Magnus.
Our smarty-pants Magnus knows this doesn't seem like the full story - some leftover pain is justified, especially if it was some black market doctor and a shoddy surgery, but what he saw during his heat is next level awful.
He asks Catarina to take a look. She confirms that yes, the organs were removed (rendering him infertile, but with a warlock boyfriend it was never much of a thought anyway) - but that's not all. Valentine had a warlock place a curse on Alec so that any time he was aroused he would be in pain. A curse she and/or Magnus are able to remove.
It's life-changing; Alec can't imagine not dreading an upcoming heat. Also, fun sexy times because he'd never really been able to explore his own body, and now he has his own and Magnus' to play with.
