A traffic accident leaves 14-year-old independent street tough Yusuke Urameshi dead. His ghost watches the scene and recalls events leading up to his death. As he accepts his situation, Boton the Grim Reaper shows up, but her pink robes, baby blue hair and cheerfully chatty nature are not what Yusuke would've expected.
In Spirit World, Yusuke meets Koenma, the toddler-appearing son of King Yama, who presents Yusuke a chance for coming back to life through a spirit egg that will feed off his soul's energy. If Yusuke's energy is good, a spirit beast will hatch that will guide him; if not good, a monster will emerge to devour him. In the meantime Yusuke struggles to tell those closest to him in the living world not to cremate his body.
While waiting for his spirit egg to hatch, Yusuke's estimation of Kazuma Kuwabara rises stemming from the rare opportunity to observe his goofy rival dealing with two teacher going out of their way to hurt him, expel him and ruin a friend's life.
Sayaka the spirit investigator checks up on Yusuke's progress, particularly looking into Yusuke's relationship with Keiko, which seems entirely one-sided. An emergency arises putting Keiko's life and Yusuke's chance for a return in jeopardy, and Yusuke must make a consequential decision.
To reclaim his body, Yusuke must enter the dreams of the three people who want him back the most and convince at least one of them to kiss him on the lips before tomorrow at midnight or else he'll remain a spirit hovering over his comatose body for the next fifty-two years.
Yusuke gets his first assignment as Spirit Detective: Three criminals have stolen dark artifacts from King Yama's vaults in Spirit World. They must be caught and the items returned - a tall order, especially for an untested, first-time Spirit Detective like Yusuke.
Hiei, the last and feistiest of the three artifact thieves, attempts to weaken Yusuke by first attacking Keiko. He starts transforming her into a demon but finds that attacking Yusuke's friends only magnifies, not weakens, Yusuke's fighting abilities, making their confrontation more interesting. Aid later comes to Yusuke from an unexpected source.
Master Genkai is retiring and looking for one last apprentice to whom to pass along her special psychic fighting powers. Koenma wants Yusuke to enter her contest for that apprenticeship, not only to gain those special powers but to discover a homicidal master criminal named Rando who's surely to be one of the contestants as well. Arriving for the qualification tests, Yusuke meets a familiar acquaintance.
Genkai's final test is a tournament between the eight finalists, fought one-on-one in her pitch black dojo until opponents are either dead or incapacitated. All the while, Yusuke wonders which one may be the homicidal Rando in disguise.
Kuwabara and Shorin face-off in the semi-finals of Genkai's tournament, which goes directly into the final match with Yusuke; however, when all seems said and done and a winner about to be declared, Rando the human-hunter finally appears, portending dire consequences for all those still alive.
After six months training with Genkai, Yusuke returns home, but there's no time to rest. Spirit World's most notorious criminals, the Four Saint Beasts, petition for immediate immigration to the living world. To force the issue, they send a continuous stream of Spirit World insects to the living world that turn humans into murderous zombies. Reluctantly, Yusuke's on the case.
Yusuke and company continue their entry into Maze Castle, confronting Byakko, a predatory white tiger demon. Kuwabara, having improved upon his spirit sword since Genkai's tournament, insists on proving himself to the others by handling this gigantic Saint Beast alone.
Kuwabara's fight with Byakko continues as the white tiger consumes the boy's spirit energy, growing larger and more threatening by the bite, while, back on Earth, Botan struggles alone against the spreading psychotic influence of the Makai insects.
With two Saint Beasts down and two to go, Yusuke's team encounters a maze in Maze Castle. Seiryu the blue ice dragon greets the boys, and Hiei wants a crack at him. Meanwhile, infections on Earth from the Makai insects are getting too much for Botan to handle.
As his team fends off an army of cultivated humans, and while Botan keeps Keiko clear of the homicidal clutches of infected humans back on Earth, Yusuke stands alone against Suzaku, leader and last of the Saint Beasts.
With Keiko running out of room to run and Yusuke's teammates unable to reach him, Suzaku and Yusuke's fight to the death continues uninterrupted, each taxing himself to the last blast of energy in order to win.
Koenma sends Yusuke a cassette tape explaining his next mission - a rescue mission. An ice apparition named Yukina is being held and tortured by exploitative human criminals because her tears turn into precious jewels.
With Yusuke, Kuwabara and Botan having unexpectedly gotten past the first demon guard, Gonzou Tarukane takes the opportunity to increase his wealth by placing bets with five ultra-wealthy underworld associates on whether or not these youthful intruders will get past the remaining demons guarding his complex, knowing the Toguro Brothers will be his ace in the hole in the end.
With Kuwabara seriously hurt, Dr. Ichigaki's control over his three human fighters is finally put to an absolute end, but the doctor has one more trick up his wicked sleeve to exact a personal victory over Yusuke and his team.
With three fighters down and no recovery time, Team Urameshi faces Team Macho, who are soon revealed as the Shinobi, mercenaries of Spirit World. Kurama decides to take on Gama, whose make-up brushes prove to be a much greater weapon than they would seem.
Paralyzed by Gama's dying curse, Kurama is entrapped to fight Touya, the ice master, in the next match. Not only is Touya a fit and determined fighter, he's Kurama's intellectual equal as well, which may make pulling off a victory against him impossible.
Yusuke finds a soul-brother in the joyful apparition Jin, against whom he must continue to fight and try to beat. Both relish a good scrap firsthand and hold nothing back in trying to pound and impress the snot out of each other.
Mr. Butajiri's endless machinations of the Dark Tournament have almost guaranteed a loss for Team Urameshi. Their last option is the severely injured but noble Kuwabara stepping into the next match against Risho, cold-hearted leader of Team Masho and master of earth. It's a decision none of Kuwabara's teammates endorse.
After feeding off Yusuke's soul energy for a year, his spirit beast finally hatches, and the result catches everybody by surprise. Soon thereafter, the mysterious masked fighter is finally ready to reveal herself to Yusuke.
Genkai's ready to transfer her powers to Yusuke, but they final requirement may be more than Yusuke can handle. Meanwhile, semi-finals of the Dark Tournament commence in a new stadium. Even with two fighters MIA, Team Urameshi's up first against Team Uratogi.
Hiei faces Kuro Momotaro, who uses steaming spheres to apply beast armor, granting him virtual invincibility. Back in the cave, the transfer of power isn't working and Genkai must remove the Spirit Wave Orb before it rips Yusuke apart.
The Hiei-Kuro Momotaro fight concludes to the satisfaction of Team Uratogi. Kurama gets the next match against a foe who uses a mystical weapon that produces a greatly unexpected result. Meanwhile, Yusuke is still writhing in the cave, being eaten alive from the inside out.
Team Urameshi suffers its first loss to Team Uratogi, and when Genkai returns as the Masked Fighter, an outcry of "foul" arises when her mask's removed and her appearance is not like before, threatening the team with disqualification.
Only Onji remains to fight for Team Uratogi, but Genkai, formerly known to all as The Masked Fighter, sees that Onji is the real masked fighter of this tournament. Outed, Onji drops his disguise and Suzuka, a narcissistic demon in clown make-up, makes his grand appearance.
It's the last of the semi-finals: Team Toguro vs. Team Gorenja. The confident Gorenja team is so easily defeated as to make the upcoming pairing of the Toguro team against Yusuke's seem like a night of college senior men taking on junior high boys. However, before the day of the finals can arrive, a pair of former lovers between the two final teams meet in private one last time.
Genkai and Younger Toguro: One last meeting between former lovers, between former teammates, between old fighters - before they try to privately kill each other well away and removed from all considerations of the tournament.
While Yusuke continues to sit in stunned grief over the loss of Genkai, Sakyo reveals his ultimate plans to the tournament directors for the trillions in gambling money he'll rake in from the Dark Tournament. It's a plan that leaves them aghast then speechless.
The final round of the Dark Tournament is just about to begin, with Team Urameshi facing Team Toguro, but each team visibly lacks a fifth fighter in order to qualify and continue, so each team is subsequently joined by a surprising fifth member.
Kurama faces off against Karasu, hoping to hold out long enough for Yoko Kurama to come forth after drinking Suzuka's juice from the Fruit of a Previous Life. That's the plan, anyway, but can Kurama survive long enough is the question.
The first match is over but not the end of problems for Team Urameshi. Bui steps up for Team Toguro; Hiei answers the challenge. Both fighters wield powers beyond their control, which will likely spell doom for quite a number of spectators in the stands.
To defeat Bui, Hiei summons up the Dragon of the Darkness Flame once again. Though he's gained a bit more control of the technique since last time he called it forth, it's still an unpredictable beast that could take out both target and attacker, as well as anyone else in the stadium.
The stadium is heavily damaged, but the next fight is up. Elder Toguro, the sadistic shape-shifter, takes special delight to revealing Genkai's death to Kuwabara, who was not told about it by any of his teammates. Ogre, meanwhile, sits in with Koto, uninvited, hoping to open a new job opportunity for himself by impressing others with commentator skills.
Kuwabara ends his fight with Elder Toguro only to redirect his unabated anger against his own team, especially Urameshi, for keeping him in the dark about Genkai's death. Before the long, anticipated battle between Yusuke and Younger Toguro can finally begin, Sakyo proposes that this next fight be the last and decisive fight of the tournament, upon which he places one last high-stakes wager.
Before even the first punch can be thrown, Younger Toguro's aura of demon energy is enough to melt the flesh off weaker apparitions in the stadium, causing Koenma to act quickly to protect Yusuke's teammates, while Puu does likewise for their friends in the stands. Several former adversaries also arrive to watch the final match.
They've initially tested each other. Now power levels above power levels are unleashed between Urameshi and Younger Toguro, heading toward full power with no one yet going down - except those poor unfortunates in the audience.
Younger Toguro's invincible demon body craves a good fight, one it hasn't been able to have in a long long time. If reaching that goal takes beating more power out of Yusuke or threatening the lives of everyone in the audience to provide the boy with enough emotional incentive, then so be it. Among those suffering, violence-overload puts Keiko in shock.