King Piccolo Saga
Yajirobe was first introduced in the King Piccolo Saga as a wandering ronin with an insatible appetite. He met Goku after the latter ate his breakfast which consisted of a huge fish. Upset, Yajirobe engaged Goku in combat.
The two had an even fight and both surprised each other with their strength and endurance. After stalemating, they were approached by the third spawn of King Piccolo named Cymbol who was after the Dragonball Yajirobe owned.
After winning a game of Rock - Paper - Scissors with Goku, Yajirobe personally challenges Cymbol in a fight. Yajirobe quickly recovers from Cymbol's physical blows and successfully evades the demon's Beam Rays as he sprints towards Cymbol and slices him with ease. Cymbol is then subsequently roasted and eaten by Yajirobe as a replacement for his lost fish.
Afterwards, Yajirobe witnesses Goku murder Tamborine in revenge for Krillin, and hides as King Piccolo brutally beats down Goku. Yajirobe helps the severely injured Goku and decides to help him get to Korin Tower after being promised special food by Goku.
With the initial assisted help from Bora, Yajirobe manages to successfully climb to the top of Korin Tower with Goku on his back. Once at the top, Yajirobe gets aquinted with Korin and introduced to the rejuvinating Senzu Beans.
Later, Yajirobe watches Goku power up from the Ultra Divine Water and King Piccolo's demise at the hands of Goku. Yajirobe manages to saves Goku's life by catching him before he hit the ground, and is seen leaving with Goku to heal his wounds at the Korin Tower.
Piccolo Jr. Saga
Three years later, Yajirobe disguises himself and enters the 23rd World Martial Arts Tournament. Unfortunately, Yajirobe is easily defeated by a disguised Kami in the last match of the preliminaries.
After the end of the Tournament, Yajirobe assists a severely injured Goku by handing him a Senzu Bean.
After a five year timeskip, Yajirobe is instructed by Kami gather all of the Z-Fighters to receive training for the arrival of two more Saiyans after the Saiyan Raditz. Yajirobe arrives at Kami House and delivers the message to Krillin who in turn alerts the others.
Once at Kami's Lookout, Yajirobe trains with Krillin, Yamcha, Chiaotzu, and Tien for a year. Despite his lack of enthusiasm and spending most of his time eating, he does end up surpassing Kami and Mr. Popo in power.
When the Saiyans finally arrive, Yajirobe initially decides to not get involved but eventually watches from the sidelines as Goku battles Vegeta and most of the Z-Fighters except Krillin and Gohan are dead.
At a seemingly hopeless moment in the battle, Yajirobe unexpectedly pulls through as he cuts of the tail of Vegeta transformed as a Great Ape from behind. This results in Vegeta losing his transformation and most of his power.
When Vegeta eventually reclaims the upper hand, Yajirobe once agains helps out by slashing Vegeta's battle armor from behind to protect Gohan. Yajirobe initially assumes he killed Vegeta and arrogantly brags about his victory. Once Vegeta regains conciousness, he brutally beats down Yajirobe as payback.
However, Yajirobe's distraction provided Gohan enough time to look at Vegeta's present Power Ball and transform into a Great Ape to eventually defeat Vegeta.
Yajirobe is seen with the group at Wunkong Hospital in West City healing from his injuries from the battle with the Saiyans. Yajirobe's injuries were relatively minor, so he wasn't kept in the hospital like Goku.
Yajirobe eventually delivers a new crop of Senzu Beans to Goku to instantly heal from his injuries and allow Goku to travel to Namek.
Yajirobe briefly appears in the Android Saga to deliver a fresh bag of Senzu Beans to the Z-Fighters but doesn't join the join out of not wanting to get killed.
While leaving in his hovercraft, Yajirobe is attacked by Androids 20 and 19. However, he survives and is carried to safety by the Z-Fighters.
Eventually, Yajirobe is seen at Korin Tower as Goku tests his new power in front of Korin to compare to Perfect Cell.
Majin Buu Saga
Yajirobe is seen continuing to stay at Korin Tower and is eventually killed by either Super Buu's Human Extinction Act, or Kid Buu's destruction of Earth from his Planet Burst attack.
Although he did not see the significance in raising his hands, Yajirobe participates in giving his energy to Goku's Super Spirit Bomb to eventually destroy Majin Buu for good.
Powers and Abilities
At the time of his introduction, Yajirobe appeared to be amongest the strongest humans alive.
Yajirobe was able to contend with Goku in an even fight and managed to kill Cymbal who was a minion of King Piccolo. Yajirobe also managed to climb up Korin's tower on his first try with Goku on his back with greater ease than Goku himself who initially struggled to climb the tower.
However, as the series goes on, Yajirobe quickly becomes outclassed and suprassed by not only Goku but even the other primary Z-Fighters and antagonists. This is the result of his laziness and cowardly nature. Despite this, Yajirobe still managed to acheive a power greater than Kami himself after bare minimal training for the Saiyans and is the strongest Earthling unable to utilize Ki.
Yajirobe is also a skilled swordsman being able to slash through tough objects or enemies thicker than the katana with ease. This played a vital role in the Saiyan Saga when Yajirobe managed to cut off Vegeta's tail while he was transformed as a Great Ape despite a monstrous power gap.
Flash and Kill - A rush attack where Yajirobe slashes an opponent into the air and then waits for the enemy to fall back down. As the enemy hits the ground, Yajirobe slashes them again.
Gigantic Rock Throw - Yajirobe uses his strength to hurl a boulder at his enemy.
Ka-Blam Hammer - Yajirobe rushes full speed at the opponent and knocks them up into the air, sending them propelling. Yajirobe then flies after them and performs a combination of four punches and smashes them down.
Ka-Blam Slicer - Yajirobe creates a very large beam of energy from his sword and launches it at the opponent.
Ki Slash - Yajirobe is able to form an energy slash from his katana. This attack is the only energy based attack Yajirobe knows.
Miracle Ka-Blam Slash - A rush attack where Yajirobe uses his katana for a flurry of sword attacks finishing with one final slice. Yajirobe used part of this move to slice off Vegeta's tail.
In the alternate timeline where Goku died of a heart virus and the Z-Fighters never learned of the Androids eventual attack, Yajirobe was one of the fighters who was killed in battle by the Androids. Gohan was the only survivor of the battle and went on to train Future Trunks.