Third person POV
As Y/n continues to train in the Hyperbolic Time Chamber, Goku intercepts Babidi and Majin Buu so that Trunks can retrieve the Dragon Radar.
Babidi: Wh-what?! What's the meaning of this?!
Goku: Buu... You're probably pretty bored right now, huh?
Buu nods excitedly and Goku smirks.
Goku: Alright then, how about a fight then?
Babidi: Don't be absurd! Buu, crush him!
Buu: ... Quiet!
Babidi: Wh-what?! Tch...!
Goku: Right then...
He drops out of Super Saiyan.
Buu: Huh? Why you go down? You no play?
Goku: We'll get to that, but I figured I'd teach you about Super Saiyans, starting with the basics. What you're seeing now is my normal state...
He powers up into a Super Saiyan again.
Goku: This is a Super Saiyan.
Buu nods excitedly as Goku introduces the form.
Goku: And this...!
He transforms into a Super Saiyan 2.
Goku: This is a Super Saiyan that has ascended past a Super Saiyan... Or, you could just call this a Super Saiyan 2.
Buu: Oooh!
Babidi: Hohum... What a useless transformation. You changed your hair, so what?
Goku smirks and chuckles, clenching his fists as he begins to power up again.
Goku: Just wait... You're going to love this, trust me!
He roars as he continues to power up.
Goku: This... Is... To go... Even further... Beyond! AAAAAAAAAAAAAAAHHHHHHHHH!!!
He continues to roar and scream as he begins transforming into a Super Saiyan 3, his hair growing out as his eyebrows disappear and he regains his pupils. As he stops screaming, he completes the transformation.
Goku: ... Sorry for the wait, I don't get to use this form very often. This is... Super Saiyan 3!
Babidi: A-ah! Wh-what...?!
Buu: Oooh! Oho!
Babidi: This power-
Buu: Hm... Buu no scared! Big hair make you big funny!
Babidi: Hm... I'm inclined to agree.
Goku: Laugh if you want, it won't change a thing.
Babidi: Oh? Perhaps Vegeta did some serious damage to your head... Or perhaps you've been driven mad by fear?
Goku: ... Perhaps.
~ Meanwhile ~
Y/n draws his hands back and fires a Galic Gun, then flies in front of it and attempts to stop it with his hands, powering up to his max in Super Saiyan 3. He successfully destroys the attack, but he reverts to his base form and collapses, panting.
Y/n: This form eats up so much energy... Maybe I should do like before the Cell Games.
He pops a Senzu Bean into his mouth and chews before swallowing, standing up and transforming into a Super Saiyan 3 again.
Y/n: I have to master this power... For the sake of the world.
~ Back with Goku ~
Goku and Buu exchange blows, Goku holding the advantage with Super Saiyan 3. However, Goku's energy was draining fast and so was his time on Earth. Goku punches Buu through an abandoned building and grits his teeth.
Goku: He's still going...
Buu flies up from the rubble and fires a barrage of Ki blasts at Goku, which he dodges. He then quickly rushes Buu and grabs his antenna before punching him, knocking him back, but he yanks the antenna and brings him back towards him. He does this for a few moments before finally punching him away and blasting him with a Kamehameha wave.
The blast created a smokescreen, but as the smoke clears, Goku can see Buu in several pieces, which then rejoin, completely reforming the Majin menace.
Goku: Tch!
Buu powers up and mirrors Goku's Kamehameha wave stance.
Goku: Wh-what?!
Buu launches a Kamehameha wave at Goku, which he barely dodges.
Goku: He can copy abilities by only seeing them once...! Incredible!
Suddenly, Goku gets a telepathic message from Piccolo.
" Goku, Trunks retrieved the Dragon Radar. You can stop. " Piccolo said
" Great! I couldn't hold this much longer anyway. " Goku replied, sighing.
Goku reverts to his base form, shocking Babidi and Majin Buu.
Babidi: Wh-what is the meaning of this?!
Goku: Sorry, I'm gonna have to cut this short.
Babidi: Then Buu will have to keep destroying, right Buu?
Buu nods and smiles.
Goku: Actually, Buu... I would like to ask you one small favor.
Buu: What? Favor?
Goku: Yes. You had a lot of fun fighting me just now, right?
Buu nods excitedly.
Goku: Well, if you hold off on destroying things for two whole days, someone even stronger and more fun than me will fight you. Sound good?
Buu: Uh-huh! Uh-huh!
Babidi: M-Majin Buu, I've heard enough, destroy him!
Goku: Why do you let Babidi boss you around like that? If I were you, I'd never take orders from that guy.
Buu nods.
Goku: So, can you wait for two days?
Buu: Mhm!
Goku: Great!
With that, Goku Instant Transmissions away.
~ Meanwhile ~
Videl stayed as close to the Hyperbolic Time Chamber as possible, her face filled with concern.
' I hope Y/n is okay... ' She thinks to herself as Goku suddenly appears, startling her and making her jump.
Videl: O-oh, you scared me!
Goku: Sorry about that... So, he's still in there, huh?
Videl nods and plays with her hair sheepishly.
Videl: Is he going to be okay?
Goku: Y/n? He's a tough guy, he'll be okay. I think he'll be glad you're here.
Videl: R-really?
Goku nods and walks away, heading towards the others to inform them about the situation.
~ With Y/n ~
Y/n pants heavily and wipes beads of sweat off his brow-less forehead.
Y/n: I'm starting to understand the limits to this form... But this overwhelming strain is hard to deal with... This is what Uncle Kakarot meant.
???: Glad you figured it out so quick. I won't have to worry.
Y/n spins on his heels and sees Goku.
Goku: Hiya.
Y/n: Uncle Kakarot? Didn't expect to see you so soon.
Goku: Yeah, figured I'd check in on your progress and I have to say you're doing amazing. Your power is incredible. In two days time, you're gonna be stronger than me.
Y/n: ... Thank you. That means a lot.
Goku: By the way, Videl is worried about you.
Y/n smiles and chuckles.
Y/n: Tell her I'm fine, will you?
Goku: Sure.
Y/n: ... Goodbye, Uncle Kakarot.
Goku: Bye bud.
They hug for a moment before they break apart, Goku exiting the Hyperbolic Time Chamber.
Y/n: ... I'll protect everyone.