Kaio-ken is a technique invented by King Kai. It basically multiplies ki and power of the user allowing them to go beyond their limits for a ‘heartbeat’. In the official anime and manga Goku is the only to have mastered the Kaio-ken technique taught by King Kai. It’s mentionable though King Kai taught Goku Kaio-ken; he himself couldn’t master it.
Kaio-ken started fading away after Goku became a super saiyan. But, we saw Goku using it from time to time on movies. Goku also used it in the anime series against Pikkon and named it the super kaio-ken.
Goku explained it to Krillen saying-
"Oh... it's the Kaioken attack. It's like a massive upsurge of energy. Everything is heightened: power, speed, even hearing and vision improve dramatically. You sort of become a super-self. But it can only be sustained for a short time, so you have to get the job done quickly."
— Goku in "Lesson Number One"
If you are thinking if other Z fighters have the ability to learn it or not; the answer is yes they do have the ability. When Goku first used Kaio-ken against Nappa, Krillen asked him if he could teach them the technique. Goku didn’t say anything like it’s not possible for them to learn. Rather he said maybe he will. So, if Goku can teach them the technique. King Kai the inventor himself could surely do it.
Now, these things raise curiosity among us.
Could it be that the Z fighters learnt Kaio-ken from King Kai during the Namek Saga?
Like Goku other Z fighters after the saiyan saga crossed the snake way. Actually they were swifter. And in many cases they were doing better than Goku in the training. Some of them stayed there longer than Goku. Which begs the question if they learnt Kaio-Ken or not?
Well, I don’t think so. If they did learn Kaio-ken they would use it in critical battle situations. If you look at the sagas after the namek saga you can see countless moments were Kaio-ken could help them. So, since they didn’t use even for once we can conclude that they didn’t learn Kaio-ken.
Would it have any real impact if they actually learnt and used Kaio-ken?
Firstly, I want to mention Krillen, Tien, Yamcha and others certainly deserves to get some new eefective techniques and increase their power. Actually, powering up by using Kaio-ken could eventually lead them to achieve higher level of transformation.
And though these characters are not really very strong power-level wise, they do have some crazy moves. Moves that can actually trouble mightiest of the opponents! For example, the Z fighters were absolutely helpless against Nappa. Yet a single destructo disk from Krillen could have killed him. If vegeta didn’t aware Nappa he would have been sliced into 2. Similarly, we see the effectiveness of this move when Krillen fought against Frieza. Hell, Krillen actually was able to hit Kid Buu with it and cut him into 2. Yes, he had regeneration power and gathered back. But, the fact that he was able to hit and have a huge impact on Kid Buu’s body gives us an idea. And how Krillen could be useful against many other opponents with his Destructo Disk! Now imagine those Destructo Disks thrown while Kaio-ken multiplied his Ki. It would be devastating.
Now coming to Tien, we all remember how he held back imperfect cell with his Tri Beams. Considering the fact that these fighters are ready to sacrifice their lives to protect earth! If Tien knew how to use Kaio-ken he could probably do Kaio-ken x 50 or kaio-ken x 100 times going beyond the capability of his body just to take out an opponent. And given how powerful Tri Beam is if it was multiplied by Kaio-ken it could have as well destroyed imperfect Cell.
Now, here’s another important thing Kaio-ken could potentially help Tien to achieve. Ever since his first appearance Tien’s third eye has been a matter of interest to all the Dragon Ball fans. And back in the Dragon Ball days when Tien ended up defeating Goku in world martial arts tournament. He actually used to get advantage for having a 3rd eye. Being able to see the movements better! So, many fans thought that Tien’s third eye is something that will be explored upon in the future. And he will be able to unlock his hidden power or something like that. And given the fact that Tien kept training and meditating being away from social life and everything; its actually surprising that he didn’t come up with 2 many moves. Because, Tien was the type of guy who liked to innovate new moves! We saw how developed new moves in such a short time in the martial arts tournaments back in the days. But, then Dragon Ball Z started and human characters started fading away. And they were eventually not explored upon. And here’s what’s interesting Kaio-ken doesn’t only increase ki or power. It also increases the ability to hear and even vision. So, Tien already has an upper hand on vision. His 3rd eye is no doubts special in Dragon Ball we saw proves of that on many occasions. And kaio-ken could actually end up helping him to unlock true potential of his 3rd eye and lead to make greater moves and transformation.
We can’t even argue that they wanted to keep it as a Goku special only; because, Goku stopped using it after becoming a super saiyan.
However, Kaio-ken or not I really want Z fighters to have a stand. Get some importance on the series. These human characters are there in the series from the very beginning and they have been training all their lives. I would actually prefer to watch them on action more than Trunks and Goten.
What do you think about this? Let me know your opinion on the comment box bellow.