Notes: This requires basic knowledge of the second TMI trilogy for context and it's heavily mixed with what I'm guessing will happen on the show and what I wish would happen on the show, but here's a brief summary: when Jonathan is brought back to life, he and Jace are bound together in the way described here (and the switches between Jonathanand Sebastianare entirely deliberate just because of that). The bloody feathers are a reference to Jonathan's message to the Institute, which was brought along with an angel wing, if I remember correctly.
Title taken from Florence and the Machine's What Kind of Man, which I strongly recommend as a soundtrack while reading this fic because it's oddly fitting regardless of the POV you choose for it.
The office was a mess. The bloody feathers, remnants of Jonathan's message, covered nearly every surface in the room and it was terrifying, worse than anything Alec had ever seen, but he couldn't bring himself to look at them just now.
Clary had warned him about this, but it hadn't been enough to lessen the shock of the parabatai rune scrawled over Jace's chest, all its lines – including the new one, the one that twisted the spell into demonic magic – a glaring red stain against his skin. In the five or so minutes since he'd climbed through the window, Jace had managed to take his shirt off to show him and had explained how the bond between them worked.
"Sebastian just wanted you to know that," he was saying, hand splayed against Alec's parabatai rune. "You can send whoever you like after him, but whatever you do to him is going to happen to me too. It's just like the parabatai bond."
"It's nothing like the parabatai bond." Alec hadn't spoken so far, torn between sounding the alarm with the hope that they could capture the man and bring him to the Institute alive and slashing through the new rune with the dagger less than an inch away from his hand on the desk behind him.
"Yes, it is. I can show you." Jace's fingers pressed into Alec's side to bring him closer and Alec could feel the dull twinge of emotion somewhere deep inside him through their bond; a bone-deep ache mixed with eagerness to comply to the orders he'd been given. "Just come with me. The Clave can't stop Sebastian; haven't they tried enough times? I told Clary the same thing, but she won't believe me. If you just follow me—"
"How can you even ask me that?" The weapon was in his grasp now, but Jace was far too close. If Alec wasn't careful, he could cause much more harm than he was hoping for. "After everything he did? I'm not going anywhere."
It was pointless; Clary had warned him about this too. She had been the first to meet Jace in this— condition and nothing had worked. Every mention of Jonathan's past actions had been ignored in favour of more attempts at coaxing her to join them. Alec should have guessed that it would be the same with him.
"He said you could say that." Jace didn't seem too bothered. "But he wanted you to know about our connection too, before you made your next move. So, parabatai." It wasn't the man he knew looking back at him, not anymore, and Alec's conviction only strengthened when Jace's fingers curled around his and he brought the blade to his own chest without an ounce of hesitation. "If you want him dead, you know what to do."
"Yes," Alec said, angling their joined hands just enough for the edge to press into Jace's skin before he pulled it down, dragging it in a long, careful line that left blood welling up in its wake. "I do."
The effect was immediate. The sudden wave of sheer terror that washed over him was almost overwhelming. Alec only managed to distance himself from it as Jace's grip on him turned desperate, digging sharply into his arms.
"Alec, I'm so sorry." His breathing was shallow and pained and Alec carefully detangled himself from his hands so that he could hold him up when Jace collapsed against his chest. "You shouldn't have let me in, I would have never—"
"It's all right." God, it hurt so much to see him like this; to feel the violent influx of emotions that had been repressed for so long now. "I'll get you to the City of Bones, Jace, and we'll fix this. We just need to open a portal—"
"No time." Jace had used his momentary distraction to wrestle the dagger away from him and press it against his own throat again, the gesture much more frantic – and determined – than it had been just a minute ago. "Jonathan must know that the connection is broken by now and once he knows, it won't last. If you kill me now, he won't have anything to hold against you."
He should have seen this coming. This had been the plan all along; this was what the message really was, not just for him, but for Clary and Isabelle and anyone else who could find themselves in this position. One way or another, you can't keep him. Alec reached for the weapon again, slow and careful as if he was trying to approach a frightened animal.
"It's just one portal, Jace, it'll take minutes. He won't be able to touch you then."
"You don't believe that. Think about it," Jace persisted, taking a step away as Alec crowded him against the window. He was too distracted with where he was going to keep track of Alec's movement too and it didn't go unnoticed. The realisation hurt, even if it was the best news Alec could imagine right now. "This is as good as it gets. The Clave will catch up with him eventually and they won't hesitate. I'll be dead anyway. Please, let me do it on my own terms."
Before he could fully process the decision he'd made, Alec had already reached for his pocket and had tackled his parabatai to the floor, wrenching the dagger away from Jace's hands and arming himself with his stele. He wouldn't be able to convince him to activate his own runes, not while he trashed under him and pulled on his hair and tried to get away, but he didn't need him to. There was plenty of space even with Jace's new rune in place.
"Don't you dare." The words were nothing but a hiss, full of venom and betrayal and desperation unlike anything Alec had ever heard in his voice. "Don't you dare do this to me, Alec, if you've ever—"
"I'm sorry." He was, and soon enough, it wouldn't matter – Jace wouldn't remember any of this – but for now, he could feel the sentiment flow through their bond and it was a small mercy to have his parabatai feel the truth of it. The drag of the stele over Jace's body was harsh, his resistance making the iratze more painful than it would have been otherwise, but it was recognisable enough to work. Alec moved on to Surefooted as soon as he was done, tracing the intricate lines blindly – he couldn't force himself to look away from Jace's eyes as he spoke. "I will get you out, but not like this. Never like this, I'm sorry."
"I hate you." The words stung, but it was the helplessness behind them that Alec couldn't quite ignore. Jace must have realised that there was nothing he could do by now, when the magic of the runes had already started spreading through his veins. "You swore an oath, parabatai, and no matter what happens now, I'll never forget—"
The faint glow of Lilith's rune returned with full force as the skin under it stitched itself together and Alec looked away, unable to watch the change as it happened. He was forced to, soon enough, by Jace's careful fingers on his jaw bringing his attention back to him once again.
"Alec." It was as if he was waking up from a dream; eyes clouded and uncertainty painted over his features. "What happened?"
"Go." Alec had to clear his throat to make himself heard, especially as Jace's eyebrows furrowed in confusion. "Go, before someone's realised that you're here."
Jace got up to his feet and pulled him along. It wasn't much of a hardship – Alec felt boneless, powerless at the sight of the change that he had caused.
"I knew you'd come to your senses." He was smiling again now; the same vacant, carefree expression he'd had when they had first met tonight. "When can I see you again?"
When, really? Alec wasn't sure he ever wanted to look his parabatai in the eye again regardless of the state he was in. "Get out of my office, Jace."
"Thank you." He let himself be pulled into a quick hug and felt Jace's lips against his cheek, the gesture – small as it was – making the urge he felt to crawl out of his skin even stronger. "Thank you, Alec, I won't forget it."
With another creak of the stained window and the draft of cold night air that followed, his parabatai was gone.