Karai (Teenage Mutant Ninja Turtles)

Karai is a fictional character appearing in American comic books published by Mirage Studios. She is usually a high-rank member of the Foot Clan outlaw ninja organization. She was originally introduced in Kevin Eastman and Peter Laird's comic book series "Teenage Mutant Ninja Turtles" in 1992. Since then, she has appeared in several different "Teenage Mutant Ninja Turtles" comics, television series, films, and video games. She is depicted as Shredder's second-in-command or adopted daughter in most versions and shares a rivalry with Leonardo.
In comics.
Mirage Studios.
The character was created by plotter Kevin Eastman, plotter-writer Peter Laird and writer-artist Jim Lawson, first appearing in cameos as an unknown woman in Mirage Studios' "Teenage Mutant Ninja Turtles" #53 (November 1992) and "Teenage Mutant Ninja Turtles" #54 (December 1992), and being named Karai in "Teenage Mutant Ninja Turtles" #55 (January 1993). She is introduced as one of the leaders of the mainstream Foot Clan in Japan (a member of its Council of Five) who came to New York City to restore order in the 1993 "City at War" story arc. Ever since Leonardo killed the Shredder (Oroku Saki), the Foot faction in NYC has been in chaos, with different groups warring with one another for ultimate control, save for Shredder's Elite, who have been carrying out seemingly motiveless attacks on the other factions. Shortly after arriving in New York, Karai captures Leonardo and offers the TMNT a deal: if the Turtles destroy the Elite, she will offer them a truce with the Foot Clan. After debate, the Turtles finally agree to seek Karai's assistance in dealing with the Elite. As they reach her skyscraper headquarters, they find dead Foot guards and the Foot's leader cradling a girl's corpse. It is revealed that the girl was Karai's daughter, and in despair, she makes Leonardo swear he will help her kill all of the Elite. During a final confrontation, five Elite face off against the Turtles, Karai, and her Foot Soldiers. The disguised Karai, wearing the Shredder's armor, orders the Elite to commit seppuku, but only one does. After an ensuing hard fight, the Turtles and Karai are the only ones left standing. Karai thanks the Turtles for their help, but they answer she owes them nothing but her word, to which she agree, saying that "no longer will the Foot Clan bother you", and returns to Japan. 
Karai never properly appears in Image Comics' "Teenage Mutant Ninja Turtles" series, despite Laird previously having considering an idea for Karai to return with "different types of ninja gear for her" as well as introducing a concept that "every new Foot soldier has a third eye ('the Eye of Karai') which is a video transceiver device that constantly relays data back to Karai's central processing computer." It is, however, revealed that she has been deposed as the leader of the Foot in Japan and is presumed to be dead. Had this series continued, Karai would have been revealed as the person behind the mask of Lady Shredder, a character introduced in the series' final issues as a third contestant vying for leadership of the Foot.
In the revival of the Mirage Studios' series by Peter Laird and Jim Lawson (without Eastman's involvement), Karai has returned to settle in New York and is using a high-tech armor. She asks Leonardo to help capture alive one of the mysterious warriors that are giving much trouble for the Foot everywhere. When Leonardo sees right through her lie about certain mystic books, even as she is usually a good liar, he suspects that something is either greatly troubling her or something is controlling her. A few weeks later, Karai visits a local high-profile nightclub, meeting Casey Jones, still longing for his wife April O'Neil who has gone on a soul-searching pilgrimage. Karai brings Jones to her private condo, where he awakens naked and remembering nothing of the previous night. He later discovers a noticeably light-hearted Karai knows something of the night before, but is hesitant to tell him. (According to Peter Laird, who shared this issue of the comic online, "what's happening with Mike, and with Karai and Casey, will have significant consequences. And I can say no more than that." Laird also noted: "It's possible that at some point we may know more about Karai's origin and her daughter. I'm not sure exactly how old Karai is, but it might just be that her daughter was adopted. In general, I consider the time span between Volume 2 and Volume 4 to be about fifteen years.")
Karai also appears in at least three stand-alone stories in the non-canon series "Tales of the Teenage Mutant Ninja Turtles", including the stories of her youth and possible future, as well as in the comic book adaptation of the 2007 animated film. According to "Complex", "since her comic book debut, Karai has become an extremely popular character, serving as the sometimes villain, sometimes uneasy ally of our fearsome foursome."
IDW Publishing.
A completely different and much younger Karai appears in IDW Publishing's ongoing, re-imagined "Teenage Mutant Ninja Turtles" reboot series by Kevin Eastman, Tom Waltz and Dan Duncan (later also Andy Kuhn and Mateus Santolouco). Duncan posted a character design sketch of her on his deviantART account, writing that he prefers to "refer to her as Shredder's girlfriend." IDW's Karai was introduced in the series' tenth main issue, published in May 2012. In 2014, Waltz said Karai is one of his favorites: "Such a cool character – tough, smart, mysterious ... you just never know what she'll do next."
The comic's Oroku Karai is a descendant of Oroku Saki (the Shredder) about 300 years after his supposed death in feudal Japan. Her backstory is told in "Villain Mini-series" #5: as a young girl, Karai found the "Ashi no Himitsu", a book detailing the secret history of the Foot Clan, in the library of her father, Oroku Yori. From there, she began to learn about the history of her ancestors in the Foot Clan and used the detailed martial arts instructions to train in the clan's unique style of ninjutsu. One night, she had a vision where Oroku Saki appeared and guided her to rebuild the Foot Clan. Having killed her own father, Karai reverted the Foot from a business enterprise to a clan of ninja warriors, training and recruiting new soldiers. Karai assisted in Oroku Saki's resurrection and remained as Chunin (second-in-command) of the clan, until Saki brainwashed Leonardo to join him, displacing Karai. Karai, in her jealousy, begins to secretly recruit for the Foot, including the creation of Bebop and Rocksteady to earn Saki's trust. After the Turtles recover Leonardo, Shredder praises her for her actions and loyalty and reinstates her as Chunin. Later, Shredder sends her to steal more resources from Krang and uses that to create Koya and Bludgeon: a mutant hawk and hammerhead shark.
After Splinter kills Shredder in issue #50, Karai offers him her sword and the role of jonin (leader) of the Foot. He accepts and gives Karai permission to travel to Japan with select soldiers to study history in order to attain honor for the Foot. She gets involved in a turf war between two Yakuza clans and is nudged by one of their leaders into embarking on a quest to recover the "Kira no Ken", an ancient sword imbued with mystical powers. When she learns that she was betrayed by him, Karai ends up taking over the entire Tokyo underworld. Under the baleful influence of the sword, she starts a vicious turf war with Splinter and the original Foot Clan, critically stabbing Splinter's faithful lieutenant Jennika when she refuses to switch sides.