This can technically, I guess, be set in either the book or show's universe, but probably relatively early in whichever verse you choose.

Memories Consume
One-shot

Their bodies were like roadmaps, lined and detailed by black runes and the scars of the ones that had faded. Some stood out harsher, deep and permanent; like burn marks, seared into their skin forever, but others faded with time, showing only if the light hit them right or if they knew it was there.

Jace knew. He knew every time Alec's arms showed that his eyes—just for a second—would drift down to look. He saw the barely-there scars of iratzes on Alec's skin, old and faded.

He remembered drawing them with shaking hands as he sobbed, clutching at Alec like it would make him stay. He remembered the smell of blood and the burning of so many runes in a concentrated area. He remembered being scared they wouldn't work and that Alec was already too far gone.

"Alec? ALEC!"

Flashes went across his vision, shaky and disjointed, like one of the horror movies Clary and Simon had made them watch to try and introduce them into mundane pop culture. Blood smeared and pooled on hardwood. His brother—his parabatai—leaned back against the wall, as if he hadn't wanted to dirty his bed when he cut into his arm with the arrow. Pale skin, too pale even for Alec. Tears.

Jace thinks he screamed, but his mind had been so full of Alec that he couldn't remember. What he remembers is rushing to him as his brain finally understood why his parabati rune had been hurting so bad. Alec, bleeding to death on his bedroom floor. Jace, terrified that he was about to lose someone else and knowing that losing Alec would hurt so much more than losing his father had.

Jace wasn't a fool. Back then, he'd known something had changed in Alec. The other boy had never been the center of attention, but when he'd turned fifteen, there had been a shift. He'd never known what it was or understood what caused it, but an already guarded Alec strengthened his walls in ways Jace hadn't known he could and he'd withdrawn.

They should have done something, he thought. Years too late, but the regret still clung to him like a second skin. It was another reminder, just as much as the faint scars on Alec's arms were; a reminder that he'd almost lost his parabatai once.

Fifteen was too young for him to have been walking around with a faded rune and a part of his soul missing.

Sixteen was too young for Alec to die.

Jace felt the phantom pain of his rune hurting at the same time he felt the memory of the pressure of Alec's weight as he held him in his arms. Skin sliding against blood. The strength of their sobs, because one's world had been shaken and the other had just given up.

Desperation. Pleading with Alec to stay with him and how could you do this and I can't lose you and we need you. Drawing healing runes until nothing remained except for the familiar markings and any evidence of that had been erased. Cleaning the blood off of Alec and helping him into clean clothes, eyes searching for anything else his parabatai may have been hiding (there hadn't been and Jace remembered wanting to cry in relief).

He'd put Alec to bed, unwilling to let him out of his sight as he cleaned the floor, scrubbing until he thought his own fingers may have been bleeding. He shivered against the memory of cold winter air coming in through the open window while he used so much bleach that their nostrils burned and their heads ached.

"I should have done it in the tub," Alec said later, his tone dead and his eyes dull when he woke up. "It would have been cleaner."

Jace had doubled over on the floor and cried. He'd never heard Alec talk like that and never did again as he made Alec swear on the Angel that he'd come to him the next time he wanted to do something like that. Alec never talked, but there were months where Alec would sit by the window in Jace's room all night. He wouldn't say a word, but the fact that he was there said enough.

Years later, Jace would understand the pain in Alec's eyes every time he offered to share the bed and why Alec would refuse.

Slowly, though, the nightly visits stopped and Alec seemed to heal. Things got better and the haunting ache in Jace's rune would fade, like even that knew they were out of the danger zone.

He let out a breath as if he were pushing the memory's weight off his chest and let his eyes search for his parabatai. Just to check, he told himself. Since Clary had come into their lives, their world had exploded so spectacularly that he never knew what way was up anymore.

He found Alec on the other side of the room and watched as Alec smiled at something Magnus said, some small quirk of his lips that lit up his eyes like Jace hadn't seen in years. He didn't understand it, whatever was going on between the two of them or why it was Magnus that was able to bring out smiles Alec's own family couldn't manage, but the gratefulness outweighed the jealousy in his gut.

Magnus touched Alec's arm, thumb brushing against the scars, and Jace's breath stopped at the same time his eyes widened, watching as Alec's eyes softened and his own hand laid over Magnus'. He knew, Jace realized. Alec had told him something he'd never even told Izzy.

Magnus said something and his parabatai's skin went pink with a blush. There was something in Alec's eyes as he looked at the warlock, but from the distance, Jace couldn't pin down the exact emotion. He thought Izzy could, though, because there was something in her smile when his eyes found hers. He didn't ask, even as curiosity churned in him.

Alec would tell him eventually.

The End