Dad?
Groot wakes up where he fell in the fields of Wakanda and immediately looks to see if his hand is intact. It's there. He's all there. He tries to decipher what really happened and what he might have hallucinated from taking a blow to the head, but everything up until the last moment felt so real. His hand turning to dust as he reached out to Rocket. His vision going in pieces like dead pixels on his ancient game console. Not feeling like he was dying, per say, but like he never existed to begin with.
Maybe reality and a bad hit to the head got a little mixed up somewhere along the way, but he knows for a fact that before he fell asleep there was a lot more chaos and a lot more people than one man with a metal arm sitting on a log nearby and polishing a gun.
"I am Groot?"
The man looks over from his busywork. "Oh, you're back." He leaves the gun on the log and walks over. "Okoye told me to wait for you while she got everyone else organized. You were with the raccoon, right?"
He should be more skeptic, but something about a messy guy with an attachment to a firearm makes Groot comfortable and he nods.
"Great. There's not much time to explain, and I'm not even completely sure what is going on, but if you're up for a fight to help your pal we need all the help we can get."
Cannon fire explodes too close to Groot and he's sent flying and tumbling to the ground. For some reason, it's then that he remembers what Rocket said about how "The Old Groot" was killed in relation to one of Thanos' ships and a fight over infinity stones and it's the last straw. All of it is too much and Groot stays curled up on the ground regretting every time he told Dad that he was a practically an adult and didn't need so much attention.
But then familiar shouting drowns out the ringing in Groot's ears, and the next thing he knows Rocket is clinging to him with more loneliness and desperation and gray hairs than he could have possibly built up in the few hours Groot has perceived since they arrived in Wakanda. One look and Groot knows he's missed something critical, but it hardly matters now as the warship aims right at the two of them.
After they miraculously made it out of that mess with their lives, Groot wonders if Rocket actually thought he could shield the relatively tall teenager from a gigantic cannon with his tiny body or if he just wanted to spend their last moments together. It's one of many things he doesn't know how to ask, and realizing he'd been gone for as long as he'd been alive only took him from knee-deep in questions to absolutely drowning.
"He shared stories about every little thing all of you did together from idiotic space adventures to the tree learning how to walk."
But right now, he only needs the answer to one.
Groot knocks on Rocket's door.
"I am Groot?" Are you okay, Dad?
'Dad.' He'd first called Rocket that in a moment of desperation, but he likes it. Peter had told him many stories about how Rocket had taken care of him from the moment he came into the world. He had also told Groot about how a dad wasn't always related to you biologically, rather 'Dad' was an earned title for someone who looked after you and loved you more than anyone else, even if they had a weird way of showing it.
That sounded like Rocket.
No response. He knocks again. "I am-"
"I'm fine. I'm working. Don't come in."
Groot remembers many occasions when he told Dad not to come into his room and he did anyway, so Groot decides to return the favor.
The lights are off. This wasn't completely unheard of for Rocket, since he had exceptional night vision and sometimes had such a brilliant idea for a weapon or explosive that he did a beeline to his work bench without bothering to turn them on, but there are no sounds of tinkering or glowing or torches or any indication that Rocket is even there at all.
Groot, not all that surprised, flicks the light switch and reveals Rocket curled up on his bunk, doing his best to pretend he hasn't been sobbing before Groot had shown up but being betrayed by sniffles and shivers. He doesn't move when Groot walks over to get a better look at him - either he knows he can't fool Groot of he's simply that despondent.
"I…" D'ast. Sometimes Groot felt like he received how vulnerable Rocket could be around him as a gift from a better version of himself who actually knew how to handle it. What would the old Groot say?
"I am Groot."
"I know he didn't mean it." Rocket stands up and dangles his legs off the side of the bed, wiping his eyes with his sleeve. Groot moves to sit beside him. "And I didn't mean that I don't want to rescue Gamora."
"I just want to do this right for once. Just one time, I want everyone to get out alive, and…"
"I am Groot."
"Yeah. Five years is a long time. You're the one to talk, too. Does this nonsense make you five years old or ten now?"
"...I am Groot?"
That gets a smirk out of Rocket. Maybe he doesn't need to be the Old Groot for this after all. "No, it does not mean you're old enough to pilot my ship now, but nice try."
"I am Groot!"
"Right. Quill's ship. That's what I said."
Groot is about to laugh, and then he sees Rocket's awkward expression and realizes that it wasn't a joke, rather than honest slip from Quill being gone so long.
Quill. Quill didn't mean it. They both knew it. They both knew he tried to take it back before Rocket cut him off and left him to Nebula's righteous indignation, but one look at Rocket and Groot knows it still hurt to hear regardless.
Maybe, Groot realizes, Rocket doesn't need any questions right now. Maybe he doesn't even need any of that sage Groot Sr. wisdom. Maybe all he needs is…
"... I am Groot?" Dad?
"What? No means no, no matter how big you make your eyes or how nicely you're about to ask. You're not getting in the driver's seat of this baby for at least another decade and that's fi-"
"I am Groot."
'Thank you for saving my life.'
Every ounce of bravado Rocket has drains away instantaneously. He stares at Groot, trying to process what he just heard.
Partially because he means it and partially because the look on Dad's face is absolutely priceless, he continues. "I am Groot." 'Thor told us about Asgard. He would have failed without you.' "I am Groot." 'We're here because you never gave up on us.' "I am Gro-"
The air is crushed out of Groot's lungs.
Rocket grabs his son and holds onto him with the same intensity he had back when he'd first found him on the battlefield, burying his face in Groot's chest and not even trying to hold back violent surges of tears anymore. His tiny frame releases sob after sob as Groot rubs circles on his back and wonders how long he's needed this hug for.
A few minutes passed before Rocket is calm enough to speak between tears.
"I… I know you're not a twig anymore and I know you're getting too old for me trying to keep you away from all the trouble we get ourselves into but… just… l-let me stay like this a little longer, okay? I just want a little more time…"
There have been a few moments in Groot's short life when he's wondered if he and the Old Groot are truly completely separate people, and this was one of them, because as Rocket holds him with every ounce of tender strength in his tiny body Groot feels like he loves his dad more than a single person could possibly love anybody.