Kazuma Kuwabara is mostly just called Kuwabara. Only his sister Shizuru, and Yukina, who he loves, call him Kazuma. Kuwabara is the second best fighter in Sarayashiki Junior High School with his rival and friend, Yusuke coming in first. He has a gang which he leads. It has him, Komada, Okubo, and Kirishima.
Spirit Detective Saga
In the beginning, Kuwabara is one of the people that appear at Yusuke's wake when he dies. He is angry and upset that he won't have the opportunity to finally defeat Yusuke in a fight. Later on, Yusuke possesses Kuwabara's body so he can talk to Keiko, who is a classmate and longtime personal friend of Yusuke's, so she can defend his body so he can come back to life.
Before Yusuke comes back to life, Kuwabara goes through some trials and tribulations with a couple of teachers at the Junior High who have some sort of personal vendetta against him. Throughout the trouble, Kuwabara shows incredible loyalty and dedication to his friends by not fighting back against some bullies from another school. Rather, he simply takes their beatings. The disembodied Yusuke helps Kuwabara through all of this by communicating with him via dreams.
Awhile after Kuwabara goes to the home of Master Genkai, an old woman that is one of the greatest human psychics ever, with Yusuke on an assignment from Koenma. He goes their to ask her about his spirit awareness which has always been abnormally high for a human, but he accidentally enters himself into her tournament, the winner of which will become her successor. He wins the first three rounds, which focus more on spiritual awareness and power than fighting, easily. During his fight with a swordsman named Musashi he discovers the ability to use the spirit sword by focusing his spirit energy into Musashi's broken sword, thus creating his signature spirit sword. His winning streak comes to an end when a powerful demon named Rando fights him. Rando shrinks Kuwabara using a legendary chant and nearly crushes him to death beneath his foot. Yusuke defeats the demon, thus winning the tournament, but he is injured badly in the process. Kuwabara is able to transfer his own spirit energy into the wounded Yusuke to save him.
Upon hearing about Yusuke's assignment to stop the Saint Beasts of Maze Castle, Kuwabara demands to go along on the journey. Once there, he is the second to fight one of the Saint Beasts after Kurama defeated Genbu. Byakko the White Tiger, Kuwabara's enemy, uses strands of his own hair to summon beasts to fight Kuwabara. Kuwabara is able to hold them off for a while with only his spirit sword, but the creatures' sheer strength proves to be too much for the human. Realizing that he'll be beaten under these circumstances, Kuwabara skewers the beasts in a circle on his spirit sword, in a technique he called the "Spirit Sword Monster Beast Donut." He then goes toe to toe with the demon Byakko. Byakko uses his demon powers to absorb Kuwabara's spirit energy from his spirit sword. Again overpowered, Kuwabara relies on his wits to win. Kuwabara super-charges his spirit sword, which overloads Byakko, causing the demon to explode and seemingly die. However, he returns to fight Kuwabara again in a lair of molten lava. Byakko employs a new ranged technique which leaves Kuwabara to jump from ledge to ledge. At one point, Kuwabara uses his spirit sword as a pole vault to avoid falling in the lava. In a moment of desperation, Kuwabara dives at Byakko, intending to fall into the lava with the demon. However, through a stroke of dumb luck, Kuwabara becomes suspended by a bandage from his ribs to a platform, saving his life while Byakko falls into the lava. Later on, Yusuke goes on to fight the leader of the Saint Beasts, Suzaku, while Kuwabara, Kurama, and Hiei fight a host of harvested humans, which are essentially zombie-like husks. After Yusuke's triumph over Suzaku, Kuwabara again saves Yusuke's life, only this time, he transfers a portion of his life energy to Yusuke instead of his spirit energy.
After the events at Maze Castle, Kuwabara and Yusuke go on a rescue mission to save the ice apparition Yukina who, unbeknownst to Kuwabara, Yusuke, and herself, is Hiei's younger sister. Yukina had been kidnapped by the crime lord Tarukane because her tears turn into extraordinarily valuable gems known as hiruseki stones. Kuwabara plays a key role in finding Yukina by leading the group of himself, Yusuke, and Botan by his pinky string, which appears as a thin red string tied to his pinky at one end and presumably Yukina at the other. It is unknown whether this is a manifestation of his spirit energy or simply a gimmick. Once the group reaches Tarukane's domain, they are met with hostility from several demon guards. Tarukane holds a video conference call with a group known as the Black Book Club, an organization of extremely wealthy individuals who gamble on matters of the spirit and demon worlds, and begins betting on the outcomes of various battles as Yusuke, Kuwabara, and Botan make their way to freeing Yukina. All the members of the club bet against Kuwabara and Yusuke consistently, except for the mysterious Sakyo. Because of this, Tarukane loses a vast amount of money to Sakyo while only reclaiming a meager portion from the other gamblers. Kuwabara and Yusuke consistently win, beating down all of the lower-leveled guards and even the Triad, which were supposed to be the strongest trio of the Apparition Gang. Yusuke defeats Miyuki and Inmaki on his own, but Gokumonki is lain low by a spiritually-charged kick from both Kuwabara and Yusuke at the same time. When Kuwabara and Yusuke get past all of the lower guards, they finally come face to face with Tarukane's trump card, the Toguro brothers. Elder Toguro uses his abilities to become a sword or shield for Younger Toguro with his super-strength to wield. However, Yusuke fires his spirit gun into Kuwabara's back, propelling him with his spirit sword forward. Kuwabara lands a direct hit on Younger Toguro, seemingly killing him. Kuwabara and Yusuke then free Yukina. She is particularly grateful to Kuwabara, comforting him when he laments the deeds that humans had done to her. It is not until later that it is revealed that neither of the Toguro brothers had actually died in the fight; rather, it was all a setup by Sakyo.
Later, Younger Toguro appears to Yusuke to invite him to the Dark Tournament, a tournament held for demons to compete and the Black Book Club to gamble again. Yusuke, Kuwabara, Hiei, and Kurama all must attend. The team's fifth fighter is the Masked Fighter.
Powers and Abilities
Kuwabara's family has a strong spiritual sense and this was passed on to him as well. He was able to sense ghosts at least since he was in elementary school. During a moment of desperation during Genkai's tournament, Kuwabara was able to manifest his Spirit Sword only needing a piece of sacred wood as a channeling point. During further training Kuwabara was able to make variations on his Spirit Sword like being able to extend it, use it as a pole vault, and firing shards, all without the aid of a prop. Kuwabara has always been a street fighter though his skill was always below Yusuke's, but he was still able to keep coming back for more. After his powers went into hibernation following the dark tournament he gained his ultimate move the Dimensional Sword where he could literally slice through dimensions. This gave him power equivalent to that of an A-Class Demon. Kuwabara was last show as the strongest spiritually aware human on the planet.
Spirit Sword: Kuwabara's first power, he summons a yellow sword constructed of his spirit energy. This energy sword is strong enough to slice through most substances.
Spirit Relfection: Kuwabara is able to deflect energy blasts in a baseball style by using his spirit sword.
Spirit Sword Javelin: Kuwabara is able to increase the length of his spirit sword to use as a a javelin for extra distance.
Double Spirit Sword: Kuwabara is able to summon two spirit swords for double the attack power, one for each hand.
Spiritual Strike: Kuwabara transforms his spirit sword into a whip like weapon that can bend and extend to hit his target. While it is in this form, Kuwabara is able to manipulate the sword, choosing where it goes.
Spirit Shuriken: Kuwabara summons many shard of his spirit sword which he fires from his hand as a long range attack.
Trial Sword: Using the hilt given to him by Suzuka, Kuwabara is able to summon this blade that can be shaped into different shapes. The blade also surrounds his body with an electric aura to increase his offense and defense. This technique is what enabled him to manipulate his spirit sword into the spirit flyswatter.
Dimension Sword: The ultimate form of Kuwabara's spirit sword that can literally cut through dimensions, psychic territories, and energy barriers with ease. Kuwabara can also halve distances using the blade giving him a form of teleportation.