Goku, Tony, Steve, Scott, and Bruce travels to 2012, the time the Chitauri Invasion happened in New York. what the others, but Goku knew is that he came to Earth the the same time this happened. The first avengers are battling the Chitauri, unknown to them that other Avengers are there.
Steve: All right, we all have our assignments. Two uptown, one stone, down. Stay low. Keep an eye on the clock.
Hulk of 2012 passes by them, smashing everything in his path. Bruce felt embarrassed.
Steve: Feel free to smash if things along the way.
Bruce: I think it's gratuitous, but whatever.
Bruce rips off his shirt and became shirtless, pretends to smash things and making roars. He then leaves to get the Time Stone as the others go to Avengers Tower.
Goku: Hey dad.
Steve: Yes, son?
Goku: Look up.
Steve looks up and sees the vortex then something came out of it. It was like a comet as it goes through the vortex and goes to another direction.
Goku: That was me. I would soon later land somewhere that you'll find me 2 years later.
Steve looks back at him and smiles as he gives him a hug and Goku hugs back. After that, they all head to the Tower and with Goku's instant transmission, he and Steve entered the building as they split up. Goku will be getting the tesseract while Steve goes for the scepter.
Goku later disguises himself as a guard, after knocking out one of them as he assisted the past versions of Tony, Thor, Pierce, his guards, and Loki. As he looks at them arguing with Alexander Pierce, someone he knew was with Hydra, over who gets to take Loki he then starts the distraction.
Goku: *fake voice* Excuse me, Mr. Pierce?
Alexander: What? What is it?
Goku: I was told something strange and flashy will occur soon.
Tony 2012: What do you mean, strange and flashy?
Goku: *normal voice* This. SOLAR FLARE!
A huge flash of light, lighter than the soon covers the lobby as everyone, including Loki were blinded and they scream of agony. Goku took this moment to grab the suitcase, containing the Tesseract and disappears with it.
After a while, everyone recovered, but they realized the tesseract was missing.
Pierce: Find this man! He may have the Tesseract!
The others set out to look for Goku, sadly they'll never find him.
*later*
Tony: So you made a big light to blind everyone temporally so you can get the Tesseract? That has to be awesome.
Goku: Yep. I used a few times, one when I rescued my dad, mom, and Sam from being captured by Hydra. To avoid it, you have to use sunglasses.
Scott: Good to now. Where's Captain Rogers.
Steve: *comms.* Coming. I just had a fight with my past counterpart, after he thought I was Loki.
Goku: Alright, dad. Can you guys do me a favor and carry this briefcase?
Tony: Why? What are you doing?
Goku: Something interesting.
Goku flies off, leaving Scott and Tony confused.
*later*
Goku heads to the location his past counterpart had landed, to meet with him. He sees his space pod and quickly lands on the ground and hides, while decreasing his powers so he won't be detected.
He later sees his younger self coming out of the crater and looking around the area he was in. He smiles at himself, knowinh that 2 years later, he'll meet his father at this same area. He uses instant transmission and disappears, leaving his part counterpart to roam around.
*later*
Goku arrives to see Bruce there with Steve, Tony and Scott.
Steve: Where did you go, Goku?
Goku: I went to see my past counterpart. I didn't talk to him, though. I see you managed to beat yourself up and get the scepter. I wish I can do that to myself, but I have my clones, so whatever.
Tony: Alright. We got the Time, Mind, and Space Stones with us, so let's go back.
They nodded as they they teleported back to the compound in their time. After arriving, they meet up with with Rhodey, Thor, and Rocket.
Rhodey: Good that you came back. You got the stuff?
Goku: *funny voice* Yeah, I got the stuff. You got the money?
Everyone laughs at the voice as Goku laughs as well, until noticing something.
Goku: Where's Clint, mom, and Nebula?
Rhodey: She was supposed to come with me, but she stayed for some reason. And Clint and Natasha haven't arrived yet.
Steve: Okay. Let's wait for them to arrive so we can start with the objective.
They nodded in agreement as they waited for the others to arrive. Then, Nebula arrives, and soon only Clint appears, with a sad look on his face.
Goku: Clint? Where's mom?
Hawkeye looks up at him, showing is depressed look on his face. It didn't take long for Goku to realize what's going on, as he couldn't sense Natasha's Ki.
Goku: *slowly starts to drop tears* Wait. Clint, don-Don't tell me that-No! She can't be! Not her! Not mom! Please! This has to be a joke! Not my mom!
Goku falls down on his knees and cries, as the others figures out that Natasha is gone. Clint explained how he got the Soul Stone, and how Natasha died. They later went outside the compound at the lake side. Goku, Tony, Thor, Clint, Steve, and Bruce mourned for Natasha Romanoff, who sacrificed herself for the Soul Stone.
Goku drops tears down his cheeks, remembering the time he first met Natasha. She was like a mother to him, who was there when he needed some guidence, helped him in his training, and was there when he needed company, as he does the same with her, too.
Tony: Do we know if she had family?
Goku: She did. Us.
Thor: What?
Tony: I just asked a question-
Thor: Yeah, you're acting like she's dead. Why are we acting like she's dead? We have the stones, right? As long as we have the stones, Cap, we can bring her back, isn't that right? So stop this shit. We're the Avengers, get it together.
Clint: We can't get her back.
Thor: Wha- what?
Clint: It can't be undone. It can't.
Thor: *dryly laughs* I'm sorry. No offense, but you're a very earthly being. Okay? We're talking about space magic. And 'can't' seems very definitive don't you think?
Clint: It can't... be undone. Or that's at least what the red floating guy had to say. Maybe you wanna go talk with him? Okay? Go grab your hammer, and you go fly and you talk to him!
Clint's anger turns to grief as Goku comforts him.
Clint: It was supposed to be me. She sacrificed her life for that goddamned stone. She bet her life on it.
Bruce got angry and grabs the bench and hurls it across the lake.
Bruce: She's not coming back. We have to make it worth it. We have to.
Steve: We will. For Natasha.
*later*
Later at the other room with the Iron Gauntlet, everyone gathered around it.
Rocket: All right. The glove's ready. Question is, who's gonna snap their freaking fingers?
Thor was about to say something, until Goku beats him right to it.
Goku: I'll go.
Everyone: What?
Goku: I'll go. I have enough power to withstand the stones. 5 years ago, I wenr toe-to-toe with Thanos, and I managed to give him several shots at him.
Bruce: No Goku. You can't.
Steve: Son. Please let's discuss about this. We don't-
Goku: Dad, I let Thanos snap his fingers and everyone we knew is gone. The only this I calm myself is to snap my fingers and everything will be back to where it was before.
Everyone stared at each other, still doubting over Goku using the Gauntlet.
Goku: Even if you don't agree, I'll do it anyway. It's my fault everyone we knew is gone, and not I'll be the one to bring them back. If I die from it, so be it.
Steve couldn't believe Goku is willing to risk his own life to bring back everyone he knew to life. Inside, he's proud that Goku has grown into the man he wanted to be all his life: A Hero. They made an agreement for Goku whield the Iron Gauntlet.
Unknown to them, Nebula from 2014 sneaks away for her mission. She activates the Quantum Portal.
Tony: Good to go?
Goku: Yeah.
Tony: You remember... everyone Thanos snapped away five years ago and just bringing them back to now, today. Don't change anything from the last five years.
Goku: Got it.
Everybody suits up as they take cover and Tony tells Friday to activate the lock down procedure. Goku slowly reach his hands to the Gauntlet as his hand enters it. As his hand enters the Gauntlet, the power surge starts to overwhelm him, but he only grunts in pain.
Steve: Son! Be careful!
Goku then charges ups his God Ki, as his aura flares and he yells, but it then turns to a monstrous roar, startling everyone. His hair starts to grow spikier.
After a while, he stops roaring and lowers his head, showing his golden eyes, shadow trim around them, and some fangs on his teeth. The others, except Steve where startled by his new appearance. Before they could say anything, Goku snaps his fingers.
After the snap, Goku was okay, with his new features staying there and he still carries the Gauntlet.
Goku: *deep voice* Did it work?
Tony: Yeah, it did.
Scott walks outside the windows and sees birds and plants. Clint's phones is ringing, it's his wife. He answers and hold his phone.
Clint: Honey...honey.
Scott: Guys... I think it worked.
Then, Goku's sense picked up something.
Steve: Son, what's wrong?
Goku: IN COMING!
Nebula of 2014 brought the Sanctuary II to the present as it shots a missle at the compound and blows up. Then a array of missiles came and destroyed the base, and everyone sinks below to the underground.