}Karai is a member and leader of the Foot Clan Japanese branch, and, following the events of City at War, became the leader of the Foot Clan New York branch. She has proved to have been both an asset and a liability to the TMNT, making her an extremely shady character.
Karai (辛い) is a Japanese word commonly used to describe the flavor "spicy/hot". However, karai can also mean "extremely severe", "harsh", "strict" or "storm". (The word also shares the same kanji (辛) as the word tsurai which means "difficult", "painful", or "cruel".)
As a child, Karai was found by Oroku Saki after her parents abandoned her. He took her in as raise her as his own, teaching her Bushido. She became his most trusted follower, even trusted to his true identity as Ch'rell and told her that the Utroms were savagely hunting him. When the Utroms fled for New York, Karai remained in charge of the Japanese Foot Clan.
When the Purple Dragons, the Mafia, and the Foot were fighting for control of New York after the Shredder's demise, Karai arrived in the city and quickly enlisted the aid of the Turtles to stop it, promising an end to the Foot’s vendetta against them in exchange for their assistance. Leonardo, believing that Karai was honorable despite her legacy, convinced Donatello and Michelangelo to aid Karai. Raphael refused, although he later recanted. Together, Karai and the Turtles eventually retook control of the New York Foot and consequently its underworld. However, the end of the story revealed that Karai had been manipulating the Turtles, and had been working with the not-dead Shredder all along. However, she showed sadness when Shredder (Chrell) vowed to get revenge on the Turtles after she had made a truce with them.
Karai’s internal conflict—her loyalty to the Turtles as fellow Bushido-practitioners vs. her loyalty to her father—was the main thrust of her Season 3 storyline, as she was pulled from both directions to take a side. She managed to stay in the graces of both sides until the Turtles faced the Shredder again in the season’s finale, where she stabbed Leonardo in the shoulder, damaging his carapace, although she later prevented the Utrom Shredder from killing the Turtles while they were unconscious. Despite her efforts, however, the Shredder was taken prisoner and exiled by the Utroms, and Karai and Foot Tech Division Head Dr. Chaplin were sent back to Earth.Karai and the Foot reappeared in Rogue in the House, Part 1, where a fully-healed Ch'rell retook control of the Foot. As his first order of business, he deployed a killer robot (disguised as Splinter) to eliminate the turtles. Realizing that their agreement with the Foot had been recanted, the turtles decided to face the Foot again in their temporary HQ—a ship stationed at the docks. Leonardo, Raphael, and Splinter were taken hostage during their encounter, and Karai was forced to fight Leonardo. Despite Leonardo’s lack of resistance, she proved unwilling to kill him.
With her father gone and dead in the eyes of the world, Karai took over the Foot and the mantle of the Shredder. Furious at what she saw as a betrayal by the Turtles, Karai plotted her revenge against them, first attacking them on the psychic plane via Foot Mystics, and later coordinating and leading an assault against them at their lair, which she believed successful. She later on faced Leo (who was not at the lair at the time of the assault), who defeated her but then departed with the warning to leave his family alone and giving her one last chance for redemption.
Karai next faced the Turtles during their attempt to retrieve a Foot artifact, an amulet called the Heart of Tengu. Despite her efforts, she was unsuccessful in stopping them. Unknown to the Turtles or Agent Bishop who initially charged them with retrieving the artifact, the Heart of Tengu was a mystical artifact that allowed the Foot to control its Elemental Mystics, who were in reality the heralds for a man-demon that had centuries ago terrorized Japan as The Shredder.