"Give up, if you honestly think that's all you can do." King Kai told Yamcha bluntly. "That's what you do when you aren't good at something, right? When someone passes you, you give up. Chasing impossible dreams... not worth anything, right?" King Kai pressed.
"I'm weak, King Kai. No matter how hard I train, how many techniques I practice, or how strong I get, every time my opponent's someone with any real power at all, I lose. Badly, King Kai." Yamcha admitted with a resigned expression on his face. It was true. Goku had been stronger than Yamcha from the moment they met, despite the differences between their training time and their ages. He'd lost easily in each of the three World Martial Arts tournaments that he'd participated in. He'd won a couple of fights, but every time that he'd fought someone with real physical power, Yamcha had lost. He'd never defeated Tien, or even Chiaotzu, despite being stronger than the latter.
"Alright. Then fight me. When I win, you give up martial arts forever." King Kai offered.
"King... Kai?" Yamcha was confused. In all the time he'd been on King Kai's planet, he'd never seen the Kai actually fight. He'd shown them techniques, sure, but he'd never exerted himself in front of them much beyond that. The idea that he'd fight Yamcha surprised both of his students.
"Don't you want to try? I'm a master of the martial arts. It's a once in a lifetime opportunity to learn your true limits." King Kai told Yamcha.
"You're right. If I'm going to give up martial arts, I might as well go out with a bang. I'll fight you, King Kai." Yamcha decided, getting into a fighting stance. Opposite from him, King Kai did the same.
"Just so you know, I won't hold back." King Kai warned.
"I'm already dead. Hit me with everything you've got!" Yamcha replied.
By now, Pigero was fully vested in the fight. He didn't have any opinion on whether or not Yamcha should give up martial arts. He didn't think it was his business, after all, but he knew that King Kai had been doing some pretty severe mental training lately, and had taught himself some new techniques that they hadn't been shown yet, probably based on Grey Mode. He wanted to see what King Kai had.
"Alright, then I'll start off with an old favorite! Wolf Fang Fist!" Yamcha shouted. The technique was one that he'd managed to improve here. Now, small blades of energy formed around his fists and feet as he unleashed an intense barrage of punches and kicks. A single hit would slice King Kai into ribbons, but the Kai just calmly dodged each and every slice.
"One." He muttered, backing off.
"I thought you said you'd hit me with everything you've got, King Kai! Don't just dodge!" Yamcha shouted, closing in again.
"You're right. It's been a while, so I'm just warming up." King Kai explained. Now, he was blocking one out of every three of Yamcha's attacks, and dodging the rest.
"So I'm just a warm-up to a guy like you! Can't say I'm surprised!" Yamcha said, backing up, realizing his attacks were useless. "Try this on for size! Spirit Zone!" Yamcha released a blast of energy at King Kai, but that's not all it was.
After seeing Pigero's deft usage of his Spirit Ball technique, Yamcha had practiced his ki manipulation more than ever. He was nowhere near Pigero's level, but he'd managed to upgrade his Spirit Ball. The result? Spirit Zone. Releasing a blast of errant Ki, the technique formed it into a half-dozen separate beams that formed a high speed, circling prison around the target. The idea behind it was similar to the Death Cage technique that Frieza had used in the future Tournament of Power, but far better for conserving energy.
"Impressive." King Kai said, standing perfectly still inside the cage. "Two!"
After shouting the number two, King Kai made his move. Brushing aside one of the energy beams that made up the Zone, he went on the attack with a flurry of punches and kicks so fast that Yamcha could only see afterimages. "Energy Trail Strike!" King Kai shouted, nailing Yamcha with a powerful kick to the gut.
Watching, Pigero instantly understood the technique, though he knew that he wasn't going to be able to replicate it easily. King Kai's Energy Trail Strike was a version of Afterimage Strike that could only be used while in a state of enhanced power, like the Kaio-ken. King Kai was using the extra energy his body wasn't able to totally control in order to give his afterimages real energy signatures to confuse Yamcha's senses.
Since it was (As far as Pigero understood) impossible to totally detach your energy from your actions, it was likely the most effective way of confusing an opponent that could sense your energy, but only for an instant. While the afterimages were given a bit of energy, they were still just traces, so all you'd need to do was train your instincts to pinpoint the strongest energy signature out of them and that'd be your guy. Yamcha couldn't do that, though, so he was forced to attempt to block every single one of King Kai's strikes, which wasn't possible for the former bandit.
"Agh!" Yamcha yelled, flying through the sky and making a crater on King Kai's planet, but King Kai wasn't done yet. "Spirit Fist!" He said it quietly, as he flew through the sky, but the effects of the technique were far from small.
'BOOM!' The energy in King Kai's fist exploded right on Yamcha's stomach before rippling through the entire planet, causing it to actually move a bit from its position, creating huge earthquakes that nobody cared about. Had Yamcha's body not dispersed the energy inside of it just a little bit, that blow would have easily gone straight through the planet before coming out the other side.
"Haah... haah." Yamcha stood shakily, spitting up blood, but smiling. "You're really... something, King Kai. If I hadn't used Kaio-ken back there, I'd have a huge hole in my chest. I forgot how much I love a good fight! Time for round two!"