It might not have been accurate to say he was flying. Yinsen could barely lift off the ground now; with his eyes closed and all his focus concentrated, he could only maintain that posture. If he wanted to move freely in the air, he still needed to keep working.
He also discovered that the Flying Technique consumed a tremendous amount of ki. No wonder that even after learning it in the early days, they still fought mostly on the ground. Goku also relied more on the Flying Nimbus to travel, largely to reduce the expenditure of his strength.
After landing back on the ground, Yinsen opened his eyes and greeted Krillin.
"You finally made it up here. Rest for a while first!"
"What are you all training?"
"The Flying Technique. Just like what you saw earlier, it lets you fly."
Krillin's mouth fell open. He had never imagined such a miraculous form of Kung Fu existed.
"There's martial arts like that?"
He turned to look around the top of Korin Tower and found that, apart from the people he recognized, there was only a completely white cat leaning on a wooden cane.
"You must be Korin, then?"
"That's right!"
"Hello, young man!"
Although Krillin was surprised that the legendary Korin was actually a cat, he quickly composed himself and greeted Korin respectfully.
After exchanging greetings, Krillin, like Yinsen and the others when they had first arrived, began receiving one-on-one instruction from Korin.
Yinsen and the others had already received theoretical guidance on ki and the Flying Technique. Their main task now was practicing how to control the ki inside their bodies. Whenever they had questions, they could ask Korin, and Korin would correct them whenever mistakes appeared in their training.
Two months after Krillin climbed Korin Tower, everyone had completed