Kurenai Yūhi

is the Konoha Jonin in charge of Team 8, which consists of Kiba Inuzuka, Shino Aburame and Hinata Hyuga. Kurenai's team specializes in tracking.

Background
Relatively little is known about her, other than the fact that she graduated from the Academy at the age of 9, took the Chunin Exam and became a Chunin at the age of 13, and that she only became a Jonin soon before the start of the series.

The anime expands on her background slightly, explaining that she had come to the village at a young age with a natural talent for genjutsu. Because of this the Third Hokage tasked Kurenai with helping to train Yakumo Kurama, another talented genjutsu user who longed to be a ninja. However, because Yakumo couldn't control her illusions and thus endangered those around her, Kurenai had to seal away her ninja abilities, in turn keeping her from ever being a ninja.

Personality
While she has a close bond with all of her students, she is especially concerned for Hinata. Kurenai knows how Hinata is viewed by her father, even though she is technically the heiress of the clan since she is the eldest child. She is also aware of her student's infatuation for Naruto Uzumaki. When Hinata tries to offer Naruto some medicine after his fight with Kiba, Naruto is hesitant to take it. Kurenai convinces him to take it. Her personality is unyielding, honest, and simple. She also says she is a "big sister type."

It had been heavily hinted that Kurenai was romantically involved with fellow Jonin Asuma Sarutobi. The two appeared together in most of their scenes, and the other characters made it a point to note this fact on several occasions. When Kakashi Hatake found the two together at a dumpling shop, he asked if they were on a date, which made Kurenai blush. During Asuma's battle with Akatsuki, Kurenai was often shown wondering about his progress, appearing anxious. When she learned of his death, she fell to her knees in remorse, and later laid flowers on his grave during his funeral. The truth of their relationship was made clear in Part II when Kurenai revealed that she is pregnant with Asuma's child.

Chunin Exams
During the Chunin Exam, Kurenai watched her pupils from the sidelines. After Shino's battle, she commented on how it suddenly got cold in the room, in reference to his rather unmerciful defeat of Zaku Abumi. During Kiba's fight with Naruto, she thought to herself (and to Kakashi) that Naruto couldn't possibly beat Kiba, only to be surprised over and over as Naruto took everything Kiba throws at him. During Hinata's fight with Neji Hyuga, she remembered the terrible relationship Hinata had with her father. She also noted the stark contrast between the current Hinata, who refused to give up, and the former Hinata, who would give up easily. When Neji was sent into a blind rage and tried to kill Hinata, Kurenai helped stop him along with every other Konoha Jonin present, except for Asuma.

She is seen again briefly during the invasion of Konoha.

Return of Itachi
Soon after Konoha proves successful in defending the village, Kurenai and Asuma discovered the Akatsuki members, Itachi Uchiha and Kisame Hoshigaki, had infiltrated the village. The two pairs engaged each other in battle, but Itachi proved to be easily capable of turning Kurenai's genjutsu against her. Before she and Asuma could be finished off, Kakashi arrived to save them, only to be caught in Itachi's Tsukuyomi, and then was saved by Might Guy.

Filler arcs
Kurenai only makes a few cameos (with Asuma) before the Kurama clan arc. Yakumo resurfaces several years after Kurenai had sealed away her kekkei genkai, which ultimately proved unsuccessful. After Yakumo creates the illusion of the Hokage Residence being struck by lightning (something everyone believes to have actually happened), Kurenai takes a temporary leave from Team 8 so that she can deal with the problem. Naruto confronts her about her involvement with Yakumo, but she simply uses a genjutsu on him to keep him busy.

As she approached Yakumo's cabin, Kurenai appeared to be trapped in a rebel's genjutsu. In actuality she had attacked her attacker in a genjutsu. She discovered that these attackers were in fact Kurama clan members intent on kidnapping Yakumo. From this point, she and the opposing ninja basically fought with nothing but Demonic Illusion: Tree Bind Death, using variations on the standard theme of the jutsu. Kurenai ended up successful until the final encounter, where she was caught off guard and cut by shuriken. The blood revealed her presence to Unkai, the temporary leader of the Kurama clan, allowing him to defeat her.

Kurenai was saved by the arrival of her team, along with Naruto and Guy. Later, when explaining to Team 8 the reasons for her departure, she claimed that the village "doesn't need any genjutsu users other than herself." This is her supposed reason for sealing Yakumo's abilities, but Shino recognized that she was lying. Yakumo, on the other hand, believed Kurenai did so in order to eventually wipe out the Kurama clan. She trapped her former sensei, Naruto, Sakura, and Team 8 in a genjutsu-created replica of the village which appeared to have been ravaged by war. Unkai was also in the illusion. Unkai, concerned by the powers Yakumo had and her continually degrading mental state as a result of being unable to control them, freed Naruto from the illusion so he could kill Yakumo. Everyone else was freed as well, except for Kurenai. Yakumo kept her trapped in the illusion in the hopes of getting revenge and answers about her past.

Naruto and the others headed back to the mountain villa and Naruto re-entered Yakumo's genjutsu world to help Kurenai. Yakumo learned that a monster named Idou that lived within her subconscious mind was the one who killed her parents. With Kurenai's help, she overcame the monster in her heart and freed Kurenai from her genjutsu. With her final mission from the Third Hokage completed, Kurenai re-assigned herself as the Jonin leader of Team 8.

Part II
Kurenai appears regularly during and following Asuma's battle with Akatsuki. After Shikamaru avenges Asuma's death by defeating Hidan, he starts taking care of Kurenai for Asuma's sake. He also vows to someday make the child his student. Because of the pregnancy, Team 8 has been led by other Jonin during its missions.

Genjutsu
As the top genjutsu specialist of the Leaf Village, most of her techniques revolve around genjutsu. Her skill at genjutsu is so great that it is able to enter the subconscious of a person to see one's true nature. The technique she is seen using the most is the Demonic Illusion: Tree Bind Death technique, where she makes the opponent believe that a tree has grown around them to keep them still. Once immobilized, Kurenai can appear from the tree to kill her target as she pleases, and is capable of using this jutsu multiple times in a row.

Trivia

 * "Yuhi" means "evening sun".
 * "Kurenai" means "crimson".
 * Kurenai's red lipstick is, in a way, a pun on her own name. The kanji for "Kurenai" can also be read as "beni" which is a word used for red makeup used traditionally in Japan to color the lips red.
 * After Kurenai is revealed to be pregnant she is seen with a ring on her finger. It is unclear if this is a wedding ring, and engagement ring, or something else.
 * During a question and answer session held at Tokyo's Jump Festa '09, Masashi Kishimoto stated that he was thinking of making Kurenai's child a girl.
 * Although her eyes are very distinct, they're not a Dojutsu.
 * Kurenai is the only one of the four principal sensei (Asuma, Kakashi, Guy, and herself) who doesn't regularly wear a flak jacket; the only time she is seen wearing one is in a flaskback with Hiashi Hyuga.