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There is one fact that Keith had to learn since he was young, a single constant that has accompanied all his life: people leave him.
As much as he wishes for them not to, as much as he fights to keep them by his side. People leave.
His mother had left him, Keith still doesn't know how or why; his father had left him, not of his own volition, but forced all the same. Loss has been defining his life since he can remember it.
Keith thoughts he would have gotten used to it.
Yet he sees Shiro's body, cold and lifeless, and he realizes that there is no getting used to this. His soul is crying, screaming at him with a desperation he hasn't felt in a long time. There is no hope to sustain him this time, no miracle that can bring him back.
His body is there, and it doesn't matter how much Keith shakes him; there is no changing fate.
"Keith," someone says, but Keith isn't listening to them.
Who has decided that there is no changing fate? Why should he accept this after all they have suffered, after all they have sacrificed?
Keith looks up at the big, gaping tear in the universe - the one they should close - and he grasps Shiro's hand one last time.
"We have to close the rift," Allura says, but Keith has another idea. If that rift can make him travel between universes, can it do something else?
It's not easy convincing the others. He almost fails several times, but Shiro was important to them too. Maybe not as much as he was for Keith, but important enough.
So, they plan. Pidge and Hunk make calculations for days on end, and Keith passes the time at Shiro's side. Sometimes Lance and Allura come, and he knows they want to stop him, they think it's too dangerous.
That Keith could die too.
He doesn't know how to make them see he doesn't care. Allura tells him he should learn to move on and she's sympathetic, talking from experience.
Keith has lost too, and he had learned to survive, but he knows this is not something he'll be able to move on from.
As many times as it takes he had promised Shiro that day, and he'll do it.
It takes a month for Pidge, Matt and Hunk to figure out every variable and they give him a little device. Activating this inside the highest concentration of Quintessence should allow Keith to travel far enough in time to be able to do... something.
"Are you even sure what you need to change?" Hunk asks, watching him, "because I think this might broke things even more." "I'll just change the last battle," Keith assures him, taking the device. It's light in his hand, and it looks almost useless. It's shaped like an earth clock, and he thinks that it's appropriate.
"Are you really sure?" Lance voice cuts across the other. His face looks serious and haunted.
Keith holds the clock tighter in his hand and nods.
He arrives minutes before the last battle begins and he knows everything that's going to happen, he thinks it will be easy. He'll make sure Shiro doesn't put himself in the trajectory of that last laser and the other will live.
After that, they don't know what will happen to Keith. Since the temporal continuum will be broken, there's a possibility he'll disappear. But he doesn't really care about it, it would just mean that the only Keith that gets to live is the one that spends his life with Shiro. It's a trade he makes gladly.
The problem is: he fails.
He manages to save Shiro from the laser-and he sees the confusion on the other's faces when they see an unknown ship fighting for them- but he doesn't have time to be happy that the moment after, Zarkon plunges at them and Shiro's ship gets cut open in half.
Keith sees the Keith of this timeline scream and Voltron charging against their enemy with blind rage.
It doesn't matter how this battle will end, Keith has already failed his mission. But he can try again.
He looks at the little clock in his hand and he restarts.
He tries so many times he has lost count now. Every time he thinks he has finally succeeded, something happens.
Once, Shiro died after the battle, when they realized that one of the Galra officers wasn't as dead as they thought he was. Once, he dies for a malfunction in the middle of battle.
Keith has tried so many times and so many possibilities and it's obvious it's not working, that fate isn't giving up.
Shiro's life might already be forfeited at this point in their life, but Keith isn't limited to this timeline.
He takes the clock and just looks at it for a second. He knows what he had promised, knows that he shouldn't do this. Keith also knows that he has already chosen in his heart.
Keith pushes the hand of the clock back and activates it.
Once he starts, he doesn't stop. He tries to save Shiro so many times only to fail at the last second, so much so that he has to wonder if, maybe, it's impossible.
Everything he does seems to be useless, and at this point he has re-lived so many lives. He tries to stay hidden, change little things, but making sure the other doesn't know it's him. He wears the BOM mask and acts in the shadow.
It hurts to see them live their life and know where it will all end up, but he has to do it. Even if he will never be able to save Shiro, can he really stop trying? As many times as it takes he had promised and he had meant every word.
In one timeline he goes to Shiro the night before the battle. He has been trying everything he could think of. He went back even before Voltron and stopped Shiro from ever joining the Kerberos crew, but he had died anyway, back on earth.
Keith feels like he's slowly going crazy, and he needs a moment, a second to remind himself why he's doing this.
He picks a night where he knows for certain he and Shiro weren't in bed together and he slips in Shiro's room, without attracting anyone's attention. The ship recognizes him, and Shiro's door is always open to him.
Shiro doesn't immediately wake up, and Keith smiles watching him sleep. He walks towards the bed and sits at the edge. He's hesitant to touch, doesn't feel like the has the right, but the last time Shiro had been a corpse, frozen.
Keith wants to feel the warmth of his skin once more.
"Keith?" Shiro asks, and he looks almost already asleep so Keith just smiles at him and finally reaches towards him. He pushes his hair out of his face and delights in the way Shiro closes his eyes at the touch.
The other is always mellower when he's sleepy and Keith loved him even more like this.
"It's everything all right?" Shiro asks, and Keith wants to tell him everything. He wants to unload his burden on him and hope that Shiro has an answer for it, but he knows what Shiro will say: Let me go.
"Don't worry, I'm fixing it," he says, and he can see the frown in Shiro's face. He hesitates a second before bending down and kissing it away.
He shouldn't do it, but he's going to travel back again soon and he needs it.
"As many times as it takes," he repeats to Shiro.
Even if I'm doomed to never actually save you.