Once a thug in his own right. He could never beat Yusuke. Eventually, they became friends with Yusuke. Through training of his Spirit Energy he now wields a sword crafted from his own spirit energy.
In school Kuwabara is ranked second toughest kid. He has always tried to be better than Yusuke, but always failed at it. He is in a gang as well yet although he acts tough he has a soft spot for kittens. He even has his own kitten named Eikichi. Although he is a punk kid he does have a code of honor that shows that he has some sense. He has a tough older sister as well. There parents however hardly ever appear. For most of Kuwabara's life he has been known for hearring ghoast that he most of the time calls "The Tickle feeling".
Kuwabara and Yusuke have been fighting since they met in High School, and for the most part, Kuwabara is always looses. He was upset by Yusuke's death, as they can never settle the score. Durning his time as a spirit, Yusuke help Kuwabara win a wager againist their jerk teachers in which Kuwabara had to get a passing score on a test, or his friend can't continue his part time job to support his family, by having dream study sessions, as well as beatup some bullies from another school who threaten to make him late for the test by possessing a school girl he knew who was knocked out by said bullies. When it was time to return back to his body, Yusuke went into Kuwabara's dream to tell him how to bring him back, by actuallying showing Kuwabara to kiss his body, naturally, Kuwabara took as jsut a bad dream.
Kuwabara and Yusuke nevered did get along until one day, Yusuke saved Kuwabra's cat, Eikichi, when he was capture by some street thugs, whose boss was really possessed by an imp, trying to corrupt Kuwabara. After that day, the two became more friends than rivals.
One of the reasons why Kuwabara went to Maze Castle was an attempt to score with Botan. They original meet at Genkai's tournament. Kuwabara gotten over Botan when he laid eyes on Hiei's sister, Yukina.
Shizuru's stirct sister. She shares acute spiritual sense with her brother, but lacks actual power. She has shown to be fearless durning the Dark Tournment, in which the demons and monsters did little to phase her. Durning the 3 Kings Arc, she pushed Kuwabara on his studies to get into a good school.
Kuwabara's signature move. He original gained this ability by channeling his energy in a broken bokken, made from a sacred tree and washed in sacred water. But after Yusuke's time training with Genkai, Kuwabara manages to create his sword without a medium. He can also use the sword in different ways, such as a pole to mack long jumps, as well as bending and shifting it into a circle, in which he used to trap Byakko's beasts in, what he likes to call, a "Monster Beast Doughnut"
A technique for his spirit sword, also obtained durnign Yusuke's training, Kuwabara can use this to increase the length of his sword to give it more use.
A technique used for the dark tournament.
A technique where Kuwabara produces small bolts of energy from his hands, similar to shuriken. He uses it only twice, as it appears to consume a large amount of spirit energy (first during his fight with Elder Toguro, and once with a lengthened version in the movie "Poltergeist Report" against Majari).
While preparing for the finals of the Dark Tournament, Suzuka gives him the sword handle that Shishiwakamaru used; though, Suzuka explains, it will be unique to him. With some practice, he is able to create a massive prismatic blade, of pure Spirit Energy, which also generates a unique, almost-electrical, aura that crackles around his entire body and improve both his offense and defense.
Kuwabara is also able to make the blade change shape as well, turning it into what he calls the Spirit Flyswatter (巨大霊気棒, Kyodai Reikibō, translated as Giant Spirit Energy Staff), which he used to pummel and defeat Elder Toguro, who could not be killed because he could shift his vital organs around his body, in the final round of the Dark Tournament.
During the chapter black arc the main villain said it could cut through territories. It is Kuwabara's best sword. This sword can drain him for an entire day after just one used. He developed this sword after his powers went into withdrawal but was brought out when he needed to save his friends from Seaman.
A man with a word of honor. He once had promised his friend ( locally dubbed as "Eric" ) that he would not fight his enemies in a week, if this was however not fulfilled, the school won't allow his friend to resume his part-time job. Kuwabara kept his promise eventhough alot of gangsters challenged him and beat him up. He also tried his best to pass the physical science test given to them by their villaneous teacher which he also gave his word that he would not fail. He tried his very best to pass it ( Yusuke's spirit also helped ) and so he and his friends did. After all these, Eric was allowed to have his part-time job. Yusuke was also impressed with the work that he had done to help Kuwabara.
When Yusuke tries to track down the demon Rando at Genkai's Tournament, Kuwabara shows up, saying that he had come so he can learn to control his increased Spiritual Awareness after hearing about Genkai's reputation (in the manga, Kuwabara mentions that his sister Shizuru had informed him about Genkai). He was largely unaware of what was going on, having only went to find a way to deal with his increased spiritual awareness. After entering in the selection process and making it through the preliminaries, Kuwabara battles against an enemy known as Musashi, in the dark, where he gains his Spirit Sword for the first time.
There, he makes it to the semifinals, where he faces Shorin. Shorin reveals himself to be the demon Yusuke had been searching for, Rando, and though Kuwabara seems to have the upper hand early on, Rando is able to beat him using an incantation he stole from a psychic, which caused Kuwabara to shrink in the middle of the fight. Yusuke fights him next, but almost dies from drowning. Luckily, Kuwabara transfers his remaining spirit energy to save him, which is enough for Yusuke to vanquish Rando.
When the Saint Beasts send a volley of Demon World Insects to
Human World, Kuwabara tags along with Yusuke, Kurama, and Hiei (both of whom are on parole), and travels to the Demon City to prevent the Saint Beasts' imminent invasion of Human World. There, to allow Yusuke to reach Suzaku in time, Kuwabara fights the Saint Beast Byakko, who absorbs Kuwabara's spirit attacks in order to become stronger. Kuwabara defeats the Saint Beast twice, one by overloading him with Spirit Energy, the other by punching the mighty beast into a lava pit. However, Byakko doesn't actually die until his teammate, Seiryu, kills him. After Yusuke defeated Suzaku, Kuwabara channeled a portion of his life energy into Yusuke to save him.
Initially, when Yusuke is given a tape by Koenma for his next mission, Kuwabara refuses to go along. However, when he sees a picture of the girl they are trying to rescue, he jumps at the chance. He helps lead them to Yukina, by means of a "pinky string" that connects the two with love. Kuwabara aids Yusuke in his defeat the Apparition Gang and their elite unit, the Triad. He fight the Younger Toguro's , whom he narrowly defeats by impaling him with his Spirit Sword, propelled by a Spirit Gun blast, fired by Yusuke, . It is later revealed that their victory was a fluke, set up by both the Toguro brothers and Sakyo, who were using them as a means to con Yukina's captor, Gonzo Tarukane, out of his fortune.
In the dark tournament Kuwabara fights more full matches than the rest of his teammates, but loses the majority of them because of ringouts. Near the end of the Tournament, Kuwabara and Kurama are approached by Suzuki (Suzuka in the English dub), the former leader of Team Uratogi. Suzuki gives Kuwabara an item to help him in the finals against Team Toguro. This item is revealed as the Tameshi no Ken, or Trial Sword, which helps him defeat Elder Toguro. During Yusuke's battle with the Younger Toguro, Kuwabara fakes his own death, with Toguro's aid, in order to draw out Yusuke's full potential.
During the first half of the Chapter Black Storyline, Kuwabara is unable to use his powers. He suspects that, like Suzuki told him, it was a side effect from using the Trial Sword. However, Genkai knows the truth: that Kuwabara's spirit awareness is so high that his own body was aware of Sensui's plan months before it happened, and has undergone a transformation to prepare for it. Kuwabara accesses his power during the battle with Sea Man, Kiyoshi Mitarai, a human teenager who is gifted with the ability to create indestrucible monsters made of water. Kuwabara's powers awaken and he gains the power to slice through dimensional barriers with a new type of energy sword, the Jigen Tou, or Dimensional Blade. He slices through the monster and wounds Sea Man, saving himself and his friends. Out of kindess, Kuwabara also spares the life of Sea Man, causing the teenager to turn good.
This powerful sword, however, is what Sensui needs to destroy the barrier blocking Demon World's strongest denizens from entering the Human World. Sensui attacks, captures Kuwabara, and plans to have another human psychic, Gourmet, eat Kuwabara and gain his power, knowing that Kuwabara would never slice the barrier willingly. However, Yusuke and team enter Sensui's lair and, after a series of ordeals, rescue their friend. Shortly afterwards, Yusuke is killed in his battle against Sensui, causing the vengeful Kuwabara to slice the barrier in order to track down Sensui and avenge his friend's death. Hiei and Kurama go with Kuwabara into Demon world, and together the three fight the powerful Sensui. Despite their best efforts, Hiei, Kurama, and Kuwabara are no match for Sensui, though he is eventually killed by a resurrected Yusuke, after he is possessed by Raizen, Yusuke's demon ancestor.
Kazuma plays a very small part in this saga. Some time after the battle against Sensui is over, and the Spirit Detectives had returned to Human World, Kuwabara learns of Yusuke's plans to go back to Demon World. His first instinct is to go with his friend, but his older sister Shizuru convinces him to stay in Human World and study for an exam so that he can get into a good high school. With this coaxing, Kuwabara decides to retire from fighting permanently and focus on his academics, allowing him to live a normal life rather than continuing to fighting demons for the rest of his life. Nonetheless, he does make a brief appearance during the Demon World Tournament, in a spiritual form in Kurama's mind, cheering Yusuke's undying fighting spirit.
At the end of the series, Kuwabara is a second year high school student at the University's prep school, called Gaikou Fuzoku High School (or Gai Tech). He has numerous female admirers, although he remains faithful to Yukina. He is also studying for his college entrance exams. His power being at A-class level, it is verified by Koenma that Kuwabara is the strongest fully-human fighter on earth. When the second Makai Tournament begins he participates in it with Yusuke, Kurama, and Hiei.