The boy's foot flashed past Roshi's face. Anticipating it, Roshi reached out to grab Kakarot's tail as it passed him by, since he still had the bad habit of leaving it loose in the midst of battle, but it was a trap.
Kakarot's tail wrapped around Roshi's wrist and tugged it into the young boy's hands. Kakarot used the momentum from Roshi's lunge to send him rolling across the water to the right, as Kakarot landed lightly on his 'feet', hovering just above the surface of the ocean as Roshi just barely managed to keep himself from falling under the waves during his tumble.
After seeing Tarble and his teammates flying so easily during the World Martial Arts tournament just over four years ago, Kakarot had taught himself how to do it. He could now fly like it was second nature.
To keep up with his student, since Kakarot, at the time, had simply been too young to let loose on the world without oversight, Master Roshi learned the flying technique for himself, too.
Since then, they'd taken to training over the ocean, similarly to how Tarble's team took serious spars. With Kakarot's power level exploding to the point where Roshi had to use his 'Pump Up' state to stand a chance against him in a straightforward fight, every time they sparred seriously, the two powerful masters would accidentally rearrange landscapes around them. Over the water, that wasn't much of a problem.
Luckily, it was only in Kakarot's Ikari Mode that the shockwaves from the duo's battles became strong enough to cause large-scale tsunamis and the like, and he struggled to reliably use it, so the fact that they hadn't figured out that it was smarter to fight up higher in the atmosphere hadn't caused any large-scale issues yet.
"You caught me by surprise." Roshi said, surprised. "You Saiyans really are amazing."
"I wanna be strong like Tarble, Master. Let's go again!"
"Kakarot, these old bones of mine…"
"I wanna go again, master! I need to get stronger! Maybe give me a bigger turtle shell, or-" Kakarot started, but Roshi cut him off.
"I can't help you anymore, Kakarot."
"...What?" The boy's eyes widened.
Roshi continued, "You've mastered all of my techniques. The Turtle School lifestyle's a part of you. I can't help you anymore. I don't have anything left to teach you, boy."
"But-But! But I still can't control my Oozaru! The red-eyed thing, either! I have so much that I just can't- So much room to grow!"
Roshi smacked Kakarot on the head with his cane, then ruffled the young Saiyan's hair. "And you can't do that… comfortable, Kakarot." He held something out for the boy. It was a glass-like bead with three stars on it. "Boy, I believe that you'll do great things. One day, you'll be at least as strong as those other Saiyans, stronger. You have so much room to grow."
"Exactly, Master! We can grow together, it'll be fun, can't you imagine it?!" Kakarot's eyes sparkled, imagining just how powerful he and his master could get.
But Roshi knew the truth. He could… probably… still beat Kakarot when he was at his best, but the boy was reaching a plateau, and Roshi himself, at least thousand times stronger than he'd been as a young man in his prime, wasn't just at a plateau.
He was at his limit. He could feel it. The eleven-year-old Saiyan was the most amazing student that Roshi had ever had, but at this point, taking care of the boy was actually holding the child back.
"This is a gift. It's a bead that I found several years ago. Your grandfather has one, which means that, now, the two greatest students I've ever had will both possess one of these little trinkets. Keep it close." Kakarot took the bead with reverence.
He'd finally graduated the Turtle School of Martial Arts.
Part of Kakarot wanted to hug the old man and ask him to keep taking care of him, to let him stay and train together with Grandpa Gohan, like they'd done together their entire lives.
Just the three of them, getting stronger and stronger forever.
But he didn't do that. Master Roshi always had Kakarot's best interest in mind. This journey… it was for the boy's own good. Things needed to change, or he wouldn't get stronger.
Kakarot returned to the Kame House to pack. About three years ago, they'd moved back from the island with the people on it to a much smaller island in the middle of the ocean.
He wasn't surprised to, when he got there, sense that Grandpa Gohan was already gone. He'd always talked about returning to his little hut, deep in the forests of Mt. Paoz.
The boy took nothing but a Hoi Poi capsule that he stored some food, clothing, and a few other basic necessities in, including the glass bead that Roshi had given him, before slipping it into his pocket, slinging his Power Pole, gifted to him by his Grandpa as a child, over his shoulder, and patting Turtle on the head as a goodbye.
Retying the blue belt on his orange gi, and checking the worn old Turtle School symbol that showed proudly on his chest, Kakarot floated out over the ocean without looking back.
His destination? Wherever the wind took him.