A/N: After Infinity War, I sought out fics positing what happened with Tony and Nebula and was happy enough with what I found that I didn't consider writing one myself. Then the A4 trailer happened . . . this is my attempt to make (some) sense of what is shown. I chose not to warn for character death because it's not technically in here, but it's definitely referenced.
Each section of the countdown is a drabble (100 words). There's one bit I borrowed from the trailer (in italics) that I didn't include in the wordcount. I have invented things for how the ship works, because they don't give us a whole lot of info in the movies.
10.
"Get up."
He blinked up at the owner of the gruff voice, surprised at the reminder that he wasn't alone in his solitude. "Why?" His voice was hoarse; he'd no idea how long he'd sat immobile in grief and pain.
"The temperature will drop when the sun sets. Unless you wish to freeze, you need to move."
He couldn't argue with that logic but couldn't stand on his own. Her grip pulling him upright was unyielding.
The sun was behind the horizon when they arrived at Star-Lord's hidden ship. When she dumped him into a chair, he promptly passed out.
9.
"Idiots!" The snarl was followed by a resounding clatter from the bowels of the ship.
Tony didn't look up from the schematic he was studying. Nebula had been prowling about and cursing for at least the hour he'd been awake, probably longer. He'd offered to help with whatever she was doing, but she'd growled and insisted he stay out of the way. So he started figuring out the computer system to pass the time. If anyone asked, he had opinions about how this piece of junk was designed.
Nebula emerged from the lower deck. "Would you rather freeze or starve?"
8.
Bottom line: Very little food or water. Enough fuel to leave the planet, possibly enough to reach the nearest inhabited system if the odds were in their favor. The pod was gone, so they had the ship and nothing else.
There wasn't really a decision to be made. Given the choice between a denuded planet and the emptiness of space, venturing into space had more potential. At the very least their communications could reach farther as they traveled.
After a day of Nebula fruitlessly scavenging for parts, they left the planet behind.
For a beautiful, fleeting moment, everything went right.
7.
Titan diminished to a speck as they left the system, they were headed full-speed toward the nearest jump point, they'd finally eaten something from their meager stores . . .
An explosion rocked the ship and flung Tony from his seat. Nebula swore and tried to keep the ship from spinning out of control. Alarms blared as a fire broke out below deck. Tony hurriedly triggered the emergency doors, sealing the fire away and venting it into space.
When the ship stabilized and the alarms quieted or were forcibly silenced, he made his way to the copilot's seat. "What the hell just happened?"
6.
The explosion took out an engine and damaged nearby systems. They could limp along on thrusters until the remaining fuel ran out, but reaching anything on the maps at that speed would take months.
They'd been broadcasting a distress call since leaving Titan, but rescue would take longer than the water would last.
Just when it seemed like the situation couldn't be any worse, Nebula cried out in rage and punched a bulkhead. "The explosion damaged the air recycler."
"It can't be fixed?"
She eyed him doubtfully. "Are you offering to try?"
"I'm something of a mechanic back on Earth."
5.
It was foreign technology but some things were universal. Tony set to work, glad to be useful.
"If this doesn't work, we'll die here," Nebula said abruptly.
"Sooner. If it works, we'll just die a few days later," Tony replied, carefully settling a wire into place. His stomach growled and he grimaced. "How much food do we have?"
"Two days."
He grunted and kept working.
"You aren't afraid to die?"
He finally glanced at her. "This isn't the first time I've faced my imminent demise. Are you?"
"No. But I have . . . regrets."
He thought of Pepper. "Yeah, join the club."
4.
The recycler needed parts they didn't have, so Tony created equivalents using most of the nanotech that wasn't holding his side together. With that handled, he tried to extend the range of the transmitter and documented his complaints with the ship's design. Nebula kept the ship on course and recorded everything they knew about Thanos.
The engine fuel and the food and water ran out the same day.
Barely two days later, a growing headache alerted Tony to the floundering oxygen level in their cabin. The environmental system's backup power checked out.
Despite his best efforts, the recycler was failing.
3.
"We run out of oxygen completely in, what, two days?" He should know this, had checked not even ten minutes ago, but the headache made it hard to remember.
"Thirty-eight hours," Nebula said flatly.
Before, her impassive expression would've given the impression that she didn't care. He knew her better now.
"So that's it, then. End of story." He sighed shallowly, resting an arm against the window frame and staring out into the cosmos. "I almost died in space once before. Guess it's going to stick this time."
Silence reigned for long moments.
"I wonder if Strange saw this part."
2.
Forming a partial helmet from his remaining nanotech took more effort than it should have.
It stared vacantly at him from the deck as he rehearsed what to say for this message in a bottle. His thoughts were hard to pin down and his tongue felt like cotton.
"Hey, Miss Potts. . . ."
He removed his fingers from the switch slowly and bowed his head. The oxygen would run out tomorrow but he wouldn't be awake that long.
He heard Nebula's steps stop next to him. He didn't look up; moving would multiply the dark spots dancing across his vision.
"You're finished?"
"Yeah, I'm finished."
1.
His remaining task was simple: buckle in and be the new communications battery. But his hands shook, the helmet slipping from his grasp as he tried to stand, and his vision greyed out almost entirely when he bent to retrieve it.
Nebula helped him fasten the harness and connect the reactor to the transmitter. Their distress call would be broadcast for decades; hopefully someone would find the ship and the information they left behind would do some good.
He fought to keep his eyes open just a little longer and was rewarded with a vision of Pepper. "Hey," he whispered.
0.
Nebula felt a pang as she watched the Terran's eyes close. He'd been a better companion than she deserved, a needed distraction from memories of Gamora and the others wakened by her presence on their ship.
He was alive, for now, but would never regain consciousness. She could last longer thanks to her inorganic parts, but with what purpose? There was nothing left to do.
Yet she lingered, her flesh fingers gently touching his shoulder.
Finally she began to turn away, then stopped. For a second, it looked like there was an incoming transmission, but it vanished.
A hallucination, surely.