When Naruto left the leaf village with the great sage Jiraiya for years Rock Lee wanted training too. He looked for his master Might Guy all over. When he found the Jonin he shouted with his usual youthful energy. "Guy-sensei please teach me more techniques so when Naruto gets back I'll show him I'm stronger."
"That's right Lee the power of youth is unbeatable. I have just the thing." Guy made the signs for summoning and brought a turtle in front of his prized pupil. "My youthful friend, take Lee to your island."
"Fine whatever, let's go kid. Reverse summoning jutsu." Lee and the turtle disappeared in a cloud of white smoke.
A single tear appeared on guys cheek as his disciple disappeared. "Lee don't die."
Meanwhile, in the Dragonball Z universe…..
Krillin was depressed since he barely did anything to beat Cell. Goku deciding to remain dead only worsened the shadow over his thoughts. He was laying in a beach chair at Roshi's pondering what to do with his life. Gohan proved he could handle any new threats that might surface. Maybe he should quit fighting and grow his hair out. His relationship was moving slowly with eighteen, so he figured if he got a real job things could improve.
While he was brooding turtle shuffled up the beach spotting him. "Hey Krillin what's wrong, You look sad?" The strongest human on earth listed his troubles. "You know I was just talking to a friend of mine. Seems he needed to find a teacher for someone. I think you would do well to remember what martial arts is truly for." Turtle moved close to his old friend and placed a flipper on him. "See you later buddy." Krillin disappeared in a puff of white smoke.
Back in the elemental nations…..
Rock Lee appeared on an island somewhere in the sea. "That turtle caught me off guard I will do two hundred pushups while standing on my head as punishment." As he performed his self designated task a loud boom knocked him off his feet. Smoke was in the air high above his head.
When the air cleared Krillin was looking at the island below. "What happened where is Kami house?" Then he saw something green bellow and started to freak out, "Sa Sai Saibaman." He started firing ki blast without uttering a word. He got lost in his memories of the fight with the sayans years ago.
Lee was about to think up more self inflicted tasks to make up for falling when the energy came. He was shocked since he didn't feel any chakra. It took all of his training to avoid being blasted to death. He had already opened the third gate to stay alive. However, his green jumpsuit was shredded and he lost all his weights.
The Z fighter regained his senses shortly after unleashing the barrage. He floated down to ground level looking for whatever he just blasted. Then he heard something behind him as the smoke cleared. "Hidden Lotus." Muscular human arms grabbed him and jumped into the air then smashed them both at the ground forming a small crater. Krillin stood taking up a defensive stance with little delay. Then he saw his opponent a kid with a bowl cut and huge eyebrows. How unfashionable now a days he thought to himself.
"Listen kid I don't want to fight you. I thought you were someone else. Your pretty good, but I think you're a bit outmatched right now." He didn't drop his guard while he waited for a response.
Strangely Rock Lee immediately dropped his guard and energetically responded. "That was amazing your power of youth is truly formidable! You must be the one Guy-sensei meant please teach me, I'm Rock Lee." The boy extended his hands with one fist covered by his other palm and bowed his head slightly in respect.
Krillin rubbed his bald head in surprise taking up a casual position. "I guess turtle was right you do need help." With more than just martial arts he thought. Lee looked about his size if a bit leaner so he pulled out a capsule and tossed it on the ground near him. After the trademark opening sound an orange uniform complete with weighted boots, wristbands and a blue shirt appeared. "Put those on kid they might be a little heavy at first, but you'll get used to it. Can't train when your half-naked, I'm Krillin by the way."
"Yes Krillin-sensei!" The fourteen year old put them on without hesitation. They were only a little heavier than his normal hidden weights.
The newly designated teacher rubbed his head in embarrassment. He reminded him some of Goku when he was younger. "Dial it back kid, we have a lot of work ahead of us."
"I'm sorry Krillin-sensei, I will do two hundred squats to make up for it." He started exercising immediately embracing the power of youth.
Well at least he has the basics down pat. Earth's mightiest human shrugged and joined in the warm up. Sometimes this sort of thing was nice too. When the pair stopped he spoke again. "Good energy Lee now let's work on building up your ki." The adult demonstrated by raising his power level a few hundred points.
The genin suddenly felt a chill of fear which he wasn't used to. His new master was even more powerful than he appeared. He was being pushed back slightly by an invisible force and the sunny sky dimmed momentarily. When his teacher stopped he shouted in joy. "Wow your power of youth is overflowing Krillin-sensei! That wasn't chakra, but the strength of it seems similar. I think I can learn it thank you so much."
"You don't even know how to build up Ki? Looks like we need to start with meditation. I sense the potential in you. A guide is all you need to master it, guess that's me." He hoped eighteen didn't kill him when he got back. However, he had sensed the kids energy spike during the battle. Maybe his pupil could teach him something as well. He was a little excited himself, new techniques could only make him a better warrior.