Hiei's early Life
When Hiei was a child his name was Emiko (boy of fire), his name was Emiko because he was born as a fire/ice demon hybrid. His father was a fire demon and his mother was of the race known as kōrime (ice maiden) (korime are an all female race). He was born a male because his mother mated with a fire demon. But since Hiei was not of the kōrime race he was shunned and banned from the village, tossed over the mountain of where the kōrime lived. Amazingly after surviving his life threatening fall he was taken in by a group of bandits, but they did not keep Hiei for long. Hiei's mother gave him a item called a "tear stone", he wore the stone to where anyone could see it, the stone had a major value, he was hoping to get in a fight. Years later when he was older he killed just for the entertainment.
He was rejected by many. After being shunned by anyone who crossed his path Hiei still wore his tear stone in plain view for anyone to see, the stone gave him a feeling of protection. Later he lost it when he fought another demon, and from there on Hiei devoted his life to finding his precious stone... Hiei later got a third eye (the eye is called the jagen) from the demonic surgeon Shigure, Shigure told him that the price he would have to pay to get the Jagen, the price would be to tell Shigure a interesting story, Hiei gave him his life story...Shigure offered Hiei some sword fighting classes, Hiei accepted (as drained because of his jagen hiei's original rank was an A-class student later reduced to a D-classes student). After a period of time Hiei soon wanted to use his "Jagen" for its original intent (to find the Land of the Korime) he also wished to find the "Tear Stone" which was taken from him in a battle. So he began his journey to find the "tear stone" (might I add the tear stone was made out of his Mothers Tears) and find the Ice village of which he came from. Once he made it to the village he tried to find his mother, however he could not find her, he could only find his mothers friend Rui (Rui was the person who was forced to throw Hiei out of the village, his mother committed suicide out of depression because she missed her son and watched his death not knowing that he was still alive). Rui also told Hiei of the existence of his twin sister Yukina who left the village for no reason, Yui said that she might have left to find her twin brother... Hiei left the village quickly and quietly after learning this information on his sister and mother. Hiei soon uses his Jagen to find the whereabouts of Yukina (and he completely ignored the tear stone, he was excited that he would be able to find his sister) Hiei went to Shigure to give him "payment" for this sword-fighting lessons they both decided that Hiei would not tell Yukina about them being related and that was Hiei's payment...
Hiei is a half ice and half fire demon. Hiei is a master swordsman and is also extremely quick on his feet. He is the master of the Dragon of the Darkness Flame. He also has a third eye called Jagan. The Jagan grants Hiei hypnosis, telepathy and remote viewing powers. Hiei asked the demon doctor Shigure to implant him with the Jagan. Shigure warned him that the surgery would drain him of all of his former strength. Hiei accepted the consequences and got the Jagen implanted onto his forehead. Shigure taught Hiei the art of swordsmanship.
Yusuke Urameshi, first day on the job
Later on Hiei stole the Shadow Sword, which allowed him to create demon slaves from whatever the blade touches. He was one of the three thieves that Koenma had sent Yusuke to go after as his first mission as Spirit Detective, and was the first to become hotheaded when Yusuke appeared, obviously not aware of the power that he had alone, let alone Kurama and the other mysterious man they had committed the crimes with. All had gone as planned, as Kurama, for whatever reason, had gotten the Forlorn Hope (dubbed "mirror of souls" in the English translation of the anime) , the other thief (who's name Hiei had never bothered-much less cared-to remember) had taken his orb of souls, and he had gotten the sword of souls, all three of which Hiei had eventually planned to take on his own anyway. However, things did not go necessarily as planned, as the new young Spirit Detective managed to take the Orb from the other thief in a matter of a week. Not exactly as the two had planned, but then again as far as he could see Kurama had not cared about the other member at all the entire time, he had actually only helped them to make sure that his mother (his human mother) get out of the hospital safely, at the cost of even his own life.
Full Demon form and still not enough for the fledgling Spirit detective
This was something that Hiei did not understand, and, because he did not understand this, he came to the "realization" that Kurama must have been weak, and, because he was weak, he needed to abandon him. Going on his own, he realized that maybe he needed the "weak" demon's help, as after finally reaching his oh so climactic battle with Yusuke, he was defeated by a mirror. He had underestimated Yusuke by a wide margin and had left himself open for attack.
When given the opportunity for a pardon from Koenma, Hiei agreed to join Kurama in assisting Yusuke in one or two cases, and his loyalty and trustworthiness were tested early and often. Little did Hiei know that this Spirit Detective would bring out the best of the half ice demon, and eventually become his greatest ally and friend within the next few months.
Four Beasts Saga
Yusuke, after being assigned to kill the Four Saint Beasts as his second real assignment, was assisted by Kurama and Hiei. Hiei and Kurama appeared in the nick of time to save them from an ambush of tiny shadow creatures that had been infected with the bug that Suzaku, leader of the four beasts ( the other three being Genbu, Shiryu, and Byakku) was planning to use on the world that turned them into violent, mindless, zombie like beings that attempted to kill anyone that Suzaku told them to. After traveling into the first floor of the castle, Hiei was put into a test of morals. As the four (Yusuke, Kazuma Kuwabara, Kurama, and himself) they were trapped by a falling ceiling of rock. Kurama and Yusuke, along with his friend Kuwabara (who Hiei had not grown too accustomed to) held up the ceiling with Hiei, but they knew that only one of them would be able to get out:Hiei, the one who was insanely fast, easily the fastest of all of them. They heard a voice from the other end of the room and they saw a small winged monster that had only one eye, and its body seemed to consist of that eye. It told them that they could only get out using Hiei, who was the only one fast enough to hit the switch before the rock crushed them all. However, this was a problem with Yusuke, as he still didn't trust Hiei. he didn't trust him to have a blade drawn, much less save his life. But, Hiei still managed to come through, though it seemed as if he was going to let them die.
After heading through the castle for some while, they came upon their first "real" opponent:Genbu, the beast of Earth and Stone. Kuwabara was nervous about it, and of course Yusuke needed to fight Suzaku, and Hiei had just done the honors of saving their lives, so Kurama stepped up to the plate when challenged by Genbu, who had recommended they just all attack him at once so he could kill them quickly.
Kuwabara had never met Kurama or Hiei, so he was iffy on the entire idea of Kurama taking on one of The Four Saint Beasts on his own. Hiei then reassured him by telling Kuwabara that the reason he had sided with Kurama back when Yusuke had just begun his detective work was because it was a much better idea to be with him than against him. Kuwabara was happy to hear this, but a little disappointed at what Kurama used to fight with:A whip. And not a traditional leather whip or chain scythe whip, but a whip made out of a rose, that he kept in his...hair?
When the dark tournament was first announced Hiei joined Yusuke's team. His team had: Kuwabara, Kurama, Hiei, Genkai, and of course Yusuke, During this time Hiei finally mastered the ability to summon the Dragon of the Darkness Flame, Hiei had many opponents and won against almost all of them, when the time finally came Yusuke fought Togoro it was a long and hard battle but after a while Yusuke won.
Hiei did not want to join Yusuke and his team, He said he had no part of being apart of the team to fulfill this mission. Yusuke was trying to take down Shinobu Sensui. Shinobu Sensui's minion "Sniper" after Hiei saved Yusuke he had to fight Yusuke to calm him down.Yusuke was furious because Shinobu Sensui had kidnapped his best friend Kuwabara. Later on Hiei made the decision to join Yusuke, but Shinobu Sensui captured Kurama and Kuwabara and they were forced to watch Yusuke Shinobu Sensui. After Yusuke defeated Sensui he gave Hiei his part of the bargain and before Hiei and even watched it he broke it in half...
When the season/arc of the show YuYu hakusho titled "Three Kings" started Mukoro had offered Hiei a job in her army. For six months Hiei underwent a survival "test" to prove if he was strong enough to be in Mukro's army, later Hiei had to fight Shigure, his own master who took him in and taught him how to sword-fight (and also surgically implanted Hiei's "Jagen"). Hiei defeated his opponent (shigure) but he was cut in half at his waist in the process (in the anime he just lost some of his arm). Later Mukoro healed Hiei's waist.Later Hiei traveled to the Human Realm and met up with Yusuke. Yusuke told Hiei about a tournament that would decide who the new demon world ruler would be. Hiei entered the tournament and made a far way in the tournament. But later he had to face Mukoro (might I add this was the final battle in the tournament). He lost to Mukoro, but got rid of her shackles. In the final Episode on Yu Yu Hakusho Hiei decides to stay in the demon realm, his job from then on was helping people who accidentally came to the demon world, he showed them their way back home to the "Human Realm"...
Powers and Abilities
Hiei is considered at the end of the series to be one of the most powerful demons in Makai with a high S-Class power rating just under the three kings of demon world. His main power is his superhuman speed that is blindingly fast. He was able to slash a demon 16 times in a flash and this was when he was a C-Class demon. Hiei is the child of an ice apparition and a fire demon allowing him to not be hurt by either temperature extreme surviving being frozen and burned alive during different fights. His implanted Jagan Eye gives him high level telepathy, telekinesis, tracking, and the ability to summon ethereal fires from both spirit and human world as well as a jangshi form that increases the effectiveness of his third eye. Beyond this Hiei is a master swordsman and hand to hand combatant.
Elemental Resistance: Hiei has a noticeable resistance to both extremes of heat and cold due to his strange parentage. He is shown taking the brunt of Seriyu's ice attacks and Zeru's flames with boredom.
Superhuman Speed: Hiei is capable of moving so fast most people cannot track his moves and kill them before they even know it. Hiei cut of Makintaro's arm and returned to his point of origin so fast that Makintaro didn't even know Hiei moved or he lost a limb. Hiei is capable of leaving an afterimage to confuse opponents.
Swordsmanship: During his early life Hiei takes up a sword has a weapon style. After receiving his Jagan Eye, Shigure the demon surgeon teaches him his techniques so he can survive the stronger areas of demon world.
Jagan Eye: Hiei's third eye in his forehead gives him telepathy, telekinesis, and mind control powers.
Jaganshi Form: The full form of the Jagan Eye where Hiei's skin turns green and he sprouts multiple eyes acroos his body. This form increases his eyes powers and his speed. This drains a lot of demon energy so Hiei doesn't use it as often after his initial fight against Yusuke.
Jaganshi Bind Curse: A binding curse Hiei uses in his Jaganshi form.
Astral Projection: Hiei is capable of separating his spirit from his body.
Dragon of the Darkness Flame: Hiei's signature attack. Hiei summons the black fire from the depths of spirit world using his own energy as bait. He then fires the blast at his opponent usually incinerating them instantly. After Hiei absorbs the dragon he gains further control over it giving him a black dragon tattoo over his right arm.
Sword of the Darkness Flame: Hiei uses his sword as a channeling point instead of his arm. This makes a lightsaber like blade that can pierce most opponents. This move is a safer alternative to the Dragon of Darkness Flame. Hiei dislikes this move to to its relative similarity to Kuwabara's Spirit Sword.
Fist of the Mortal Flame: Hiei surrounds his fist in a fire from the human world and pummels his opponent close range.
Mortal Flame Flamethrower: Hiei uses the Mortal Flame for a ranged attack to burn his opponent.
Black Dragon Wave: Hiei's most powerful technique that can only be done in his Jaganshi form. Hiei summons multiple dragons to cause massive destruction and can fully control who the dragons attack.