In the end Loki begged help of Banner. He hated to approach Banner for anything; even after months of helping Thor and his Avenger friends restore order to planets that had had their populations doubled overnight, Banner didn't seem to quite trust him.
And even though it had been over a decade since Banner had put him through the floor of Stark's tower hard enough to liberate his mind from the mind stone (and nearly liberate his breath from his body)… he still didn't quite trust Banner.
But this would be delicate. He needed to time his arrival to the minute and to the foot. If he arrived too early, he'd be walking into a battle. If he arrived too late, he'd find just the ruins of a destroyed ship, and Thor floating off through space alone.
Banner could help: he had actually been there for most of it, and he knew how to work the time machine with a precision that Loki could never hope to duplicate alone.
Fortunately, Banner seemed receptive.
"Look, I get it," he said. Patted Loki's shoulder with a massive green paw. "Seeing your own death, understanding your own death, is a really powerful idea, okay. I want to help."
Clearly there was a but. He braced for it.
"But you're shady, Loki." Banner added at last, with a regretful smile. "I mean sorry, but that's kind of your trademark, right? So if I help you go back… and you… do something…?"
"What would I possibly do?"
Banner shrugged. "I don't know, man, but here you are. When you're supposed to be dead."
Loki stepped close. "That's right," he said, "Here I am." He spun around, showing off his haircut, his clothes. "I'm alive and I like it that way. Why would I cause any trouble for myself or you or anything about this reality?"
Banner still shook his head.
"I can give you my word, if that means anything?"
Banner laughed sadly. "Sorry. No offense."
"None taken." Lie. "Look… you can come with me if you want," he suggested. "I honestly just want to see what happens, and come back. I swear I will not touch anything, or speak to anyone, or do anything other than look. Just look. I swear it."
"I am not going back to that ship."
Understandable. "All right, well. I need to." Banner was still. "Please. I need to know."
He arrived at the right time, and in the right place: behind the remains of a snarl of piping, by a broken steam-pipe whose billowing clouds masked any poof of arrival. He peeked out.
His past self was a prisoner of Thanos's lackeys-…
And could see him. Did a double-take. Damn him for his sharp eyes.
Loki put a finger to his lips. His past self frowned. Nodded. Wiped his expression clean, and stopped staring at him.
Maybe he thought he was imagining it, Loki thought… but no. His past self raised a hand and curled his fingers, quick and halfway – a hint of his old time-travel gesture. Who knew what chaos would ensue if he didn't respond – what if his past self drew everyone's attention to him? – so Loki shifted into the light briefly and performed the second half of the sign, before fading back into the shadows, drawing spells of concealment over himself as he did. Nothing to see here.
He was annoyed: now that his past self had seen someone dropping in from the future he'd behave differently, and Loki would never know what had really happened.
"The Tesseract, or your brother's head," Thanos was saying. "I assume you have a preference?"
His past self glanced at him as if to check his opinion. He shook his head, meaning don't look at me, but apparently the gesture was misunderstood. "Oh, I do. Kill away."
No. Thor had told him that he'd agreed to give up the Tesseract! As he absolutely should have; if his past self didn't capitulate soon they were all going to watch Thor murdered. He shook his head frantically, made a cutting gesture across his own throat. Stop this.
His past self didn't really need the hint; he capitulated on his own. "All right stop!"
Loki ducked back behind the pipes and tried to regroup. This was awful. Not only was he watching Thanos brutalize his ship and his brother and himself, but now, his past self was apparently looking to him for guidance on what to do.
Don't ask me. I have no idea. He stayed hidden, listening to his past self try and tip Thor off that they had a time traveler, and then set up a distraction so that the Hulk could attack. It was pretty decent delivery. Good on him.
But the Hulk failed, and Thanos prevailed, and soon Heimdall was dead and Banner gone and Thor immobilized. Now he was flying blind – Banner had recollected the early parts of the scene with scientific precision, but this last bit he had gotten only from a washed-up, drunken version of Thor who was digging into trauma-tinged memories more than five years old. His Thor had never seen this day, and could tell him nothing.
So he had no idea what was going to happen. He crept around the edges of the destroyed chamber to try and get a closer look-
And tripped over himself. His past self, flung away and forgotten, watching from the sidelines.
They stared at each other.
"Are you alone?" his past self breathed – less than a whisper.
He nodded. What else was he supposed to do?
"Stop waiting for the perfect chance; we're out of time," his past self breathed, quickly. So quickly there was no time to argue with him. "He just took his armor off. I'll distract him again. Your knives, his back. Don't miss."
And then he was gone, stepping out into the room, volunteering to lead Thanos's people down to earth. Seeking Thanos's attention - and then drawing a knife to require it.
When Bearded Thor had first told him that he'd tried to just stab Thanos in the face, from the front, he'd had no idea what he could have been thinking.
Now he knew. Now he knew how he'd guessed they would time travel, and why he'd been so stupid as to engage Thanos hand to hand.
This was his fault. His fault for being here, his fault for causing himself to take stupid actions, his own damn fault for not making it out alive. I'm sorry.
His past self, frozen and seized, was looking to him for help, but if he revealed himself there was no guarantee that his suit would survive a fight intact, no guarantee that he'd get a chance to use the wristwatch to escape. He couldn't risk it. I'm so sorry. Shaking his head. He pointed to himself and to his eyes. I'm only here to watch.
Thanos was lifting by the neck, as Thor had said. He wanted to duck down and hide again, but his past self had locked gaze with him and he couldn't bring himself to break it. Help me. Help. I need help. He could see it in his eyes – he never begged, but he was begging now – and still he did nothing. The depth of the betrayal was unfathomable. What must I think of me?
His past self used its last words to answer that question for him: "You will never be a god." He heard his own neck break.
So apparently he'd died begging for help that never came, died abandoned, died hating himself. There: now he knew. His hands were shaking almost too much to operate the wristwatch. He got it done just before the ship disintegrated. Swore he wouldn't time-travel again.
The End.
There we go. Sorry it's a bummer! Envision brainy!Hulk giving him a big green hug when he returns to the future, if that helps.
Let me know what you thought of this. Again: thanks for reading, and SORRY!