Story

Kazuma Kuwabara was Yusuke's rival at first, being second toughest punk at Sarayashiki Jr High. He fought with Yusuke nearly every single day (and lost) in the hopes of defeating him.
In the anime, when Yusuke dies, Kuwabara stomps in at his wake, demanding that he crawl out of his coffin and fight him like a real man. As his comrades pulled him away, he let loose some tears and cried out 'No', which gives us the idea that Kuwabara cared deeply for Yusuke as one his rare friends, which is very different then the manga, where it seems all he wants to do his fight him.

We see a part in the show (Anime: Episode 3 | Manga: Chapter 7) that solely reflects on Kuwabara's friendly and loyal nature. Okubo's, one of his friends, part time job is in jeporday when rat face, Mr. Akashi threatens to take it away from him for fighting.
He makes a deal with Kuwabara and his gang that they musn't fight for an entire week and get a 50% score or higher on their next science test. Kuwabara says he'll do it, but his friends worry, since he loves fighting and isn't exactly bright.
Yusuke (as a ghost) doesn't believe he can do it, but he sees that Kuwabara has rock-hard determination and watches over him as he refrains from fighting and studies hard. His work pays off as he scores 53% on his test and Okubo gets to keep his job.

After Yusuke ressurects from the dead, he aids Kuwabara by saving his beloved kitten, Eikichi, and Kuwabara is secretly grateful to him. He really doesn't get involved with fighting until (Anime: Episode 9 | Manga: Chapter 24) Yusuke goes to Genkai's Tournament to become her pupil. (He's actually there for a mission to stop an under-cover demon).
He finds Kuwabara there and the boy explains that he came to the old phsycic for advice on how to control his sixth sense, or spirit awareness. Unfortunately, he came on the day the trails for Genkai's new apprentice was to be chosen, and ends up fighting with the rest of the combatants.
Kuwabara first shows spirit power in his first fight with Musashi, a demon slayer, by using a broken piece of Musahi's wooden sword to create his aura sword, or Rei Ken, ( which means Spirit sword).
In his second fight, with Shorin (Rando in disguise), he ends up becoming the size of a doll and almost killed when Shorin squeezes him inside of his palm. In a fit of rage, Yusuke defeats Shorin aka Rando after a gruesome battle and avenges his friend.

Then, after six horrible months of training with Genkai, Yusuke gets a mission to destroy a Makai whistle that's being held by a deadly group known as the Saint Beasts who live in Maze Castle. Kuwabara willingly goes with him, and with the aid of Kurama and Hiei, the four triumph in Maze Castle.
During these episodes, he fights against a giant white tiger demon named Byyako, who was very powerful. Out of all the episodes, his fight with the white tiger was the second longest, dragging for one and half episodes. He also introduces his Spirit Javelin during his fight with Byyako.

After Maze Castle, Yusuke receives a mission from Koenma to save an Ice Maiden who was imprisoned by a greedy human crimelord for the precious gems she creates whenever she cries. Yusuke asks Kuwabara if he could watch the video tape at his house and Kuwabara says there was no way in hell he would risk his life again in another wacky mission.
At the first sight of her on his television screen, Kuwabara fell in head over heels in love and demanded that they go save the girl, completely forgetting about his dramatic speech of not going in the first place. There, Yusuke and Kuwabara fight with the Toguro Brothers and save Yukina.

A few days prior to the Yukina Arc, Yusuke meets Younger Toguro (whom he thought they had killed) in the streets of Tokyo and is invited to participate in the Dark Tournament. For two months, all four members train endlessly and head on to the tournament. Kuwabara introduces his Double Spirit Sword, Power of Love, Spirit Shards attack, and Spirit Flyswatter in this saga. He fights his enemies in this order: Rinku, M1/M2/M3, Risho, Shishiwakamaru, Onji, and Older Toguro.

During the Chapter Black Saga, Kuwabara is left with no Spirit Energy through out episodes 67-75. At episode 76, he fights with one of Sensui's seven, an adolecent nicknamed 'Seaman'.
Seaman threatens the life of Kuwabara's three dear friends and traps all four of them within his water monster/territory. Kuwabara grows so deterimined and angry when his friends run out of breath that he destroys Seaman's territory (which is not possible) by cutting through two dimensions at once with is Dimension Blade, or Jigen Tou in Japanese.
After defeating Seaman, Kuwabara brings his three friends and the injured teen to Yusuke's aparment in order for them (and himself) to be healed. It turns out that Sensui was looking for someone who could slice through the Makai Barrier, and that's what Kuwabara's new technique can do.
Sensui kidnaps Kuwabara, and is used as bait for Yusuke and the others. He was originally supposed to be eaten by Gourmet so that he could have Kuwabara's powers, but they're stopped by Yusuke and the rest.

KUWABARA DOES NOT REALLY APPEAR IN THE LAST SAGA, THE THREE KINGS

Items Kuwabara uses in the Dark Tournament:

This sword hilt was given to Kuwabara by Suzuka after the semifinals were over. He originaly gave it to Shishiwakamaru, but it became the Banshee Balde for him. For Kuwabara, it turned into...

...THIS! It becomes a bigger and badder version of his Spirit Sword that increases his offence and defence power. It also became...

...THE SPIRIT FLYSWATTER! He expands all of his energy to use this move! This is the only time he uses it, and it defeats Elder Toguro in one foul swoop.

For a list of Kuwabara's attacks, please refer to the Attack List section, located under 'Kuwabara'

LAST UPDATED AND FINISHED ON: NOVEMBER 6, 2006