Teenage Mutant Ninja Turtles is an American action animated television series developed by Ciro Nieli, Joshua Sternin, and Jennifer Ventimilia for Nickelodeon, based on the Teenage Mutant Ninja Turtles characters created by Kevin Eastman and Peter Laird. The series begins with the Turtles emerging from their sewer home for the first time, using their ninjutsu training to fight enemies in present-day New York City. The series ran in the United States from September 28, 2012, to November 12, 2017.
The series was first announced in October 2009, following the news that Nickelodeon's parent company Viacom had acquired the rights to the Teenage Mutant Ninja Turtles franchise. The show was created to reach a core audience of boys aged 6 to 11; it was one half of Nickelodeon's strategy to reboot two established brands for new viewers, coinciding with Nickelodeon Animation Studio's development of new Winx Club episodes for girls. It was produced by Nickelodeon Animation Studio and LowBar Productions. Bardel Entertainment and Technicolor Animation India handled layout and CG animation services.
During the months leading to its premiere, Nickelodeon and Playmates Toys released lines of merchandise featuring the new character designs. The two-part premiere took place on September 28 and September 29, 2012, reaching 3.9 million viewers. The debut ratings were the highest for a Nickelodeon animated series since 2009, leading to a second season pickup in October 2012. Three more seasons followed; the fifth and final season was rebranded as Tales of the Teenage Mutant Ninja Turtles and did not fully air on Nickelodeon, as episodes 115–121 premiered on its sister channel Nicktoons.
Plot Season 1
Ninjutsu master Hamato Yoshi (Splinter) is carrying his four pet turtles through the streets of Manhattan when he encounters members of an alien race called the Kraang. During an altercation with these aliens, Yoshi and the turtles are exposed to the Kraang's chemical, called mutagen, which causes organic beings to undergo major physical transformations. Yoshi takes on characteristics of a brown rat and the turtles take on human characteristics. Yoshi retreats to the New York City sewers, where he raises the four turtles as his sons and imparts to them his knowledge of ninjutsu.
Now teenagers, the turtles (Leonardo, Raphael, Donatello and Michelangelo) venture to the surface for the first time and learn that the Kraang are using the mutagen as part of their plan to take over New York City. They befriend the teenage April O'Neil after she and her psychologist father Kirby are abducted by the Kraang. Donatello, who has developed a crush on April, is able to rescue her. While Kirby remains a prisoner of the Kraang, April becomes an ally of the turtles, who try to help her locate her father. April is also trained by Splinter to be a kunoichi, a female ninja.
After learning of Splinter's and the turtles' presence in New York, Splinter's adoptive brother and long-time enemy Shredder travels there from Japan and orders his birth clan, the Foot to track down Splinter and his sons, and put an end to their clan. Learning about the Kraang's presence through his adopted daughter Karai, Shredder enters an alliance with the aliens to destroy their mutual enemies in the Hamato Clan.
The turtles later discover that the Kraang came to Earth from Dimension X and built their headquarters with a company called TCRI and are plotting to use the mutagen and a set of Kraang-like powers that April was born with to convert Earth into a planet suitable for their race. After the turtles rescue Kirby, the Kraang invade New York, but the turtles and April emerge triumphant when they send the Technodrome, the Kraang leader Kraang Prime's ship, crashing into the sea. Meanwhile, Splinter battles Shredder and learns that Karai is his daughter, Hamato Miwa, who was kidnapped by Shredder and who believes that Splinter killed her mother. The season ends with the turtles celebrating their victory over the Kraang as Splinter hides the secret of Miwa from them.
Season 2
The turtles struggle to contain an outbreak of mutations that occurs thanks to the leftover mutagen from the thwarted Kraang invasion. Kirby is among the victims of the outbreak, and a misunderstanding leads April to break off her friendship with the turtles. However, the turtles are able to earn her forgiveness when they save her from Karai, who has taken temporary command of the Foot while the Shredder is away in Japan. Along with April came her new friend Casey Jones, who helps repel an assault on the turtles' lair. Kirby is eventually restored to his human form when Donatello manages to concoct another Kraang chemical called retro-mutagen, which causes organic beings to reverse their major physical transformations.
Meanwhile, Shredder returns from Japan with the mutated Japanese bounty hunter Tiger Claw as his new second-in-command. Tiger Claw is sent through a portal to the 1987–1996 animated series reality, but later returns to the 2012 reality.
During a battle with the turtles, Karai is informed of her true nature by Leonardo (who has developed a crush on her since season 1), but she is too reluctant to accept it. When she is taken to the lair, she finally realizes the truth and disowns Shredder, who responds by imprisoning her. Repeated attempts to free Karai ultimately succeed, but Shredder captures her again and uses her as bait to kill the Hamato Clan. However, Karai is inadvertently mutated into a horned viper.
In response to this, Shredder has the Foot Clan help the Kraang, who have just perfected the previously unstable mutagen, launch a second invasion of New York, starting by destroying the turtles' lair courtesy of April's friend Irma, who was really an elite Kraang spy named Kraang Subprime, and forcing them to abandon it. The Kraang begin mutating New York's populace, including Kirby, despite the efforts of Earth's military and the turtles. Leonardo is gravely wounded when he is ambushed by the entire Foot, and Splinter is seemingly killed during a battle with Shredder. The turtles, April, and Casey are forced to flee to the O'Neil family's summer home in Upstate New York as the Kraang conquers Manhattan.
Season 3
The group takes refuge at the O'Neil family's summer home in North Hampton to recuperate from their loss at the hands of the Kraang and the Foot Clan. Leonardo takes an extended amount of time to recover, but guided by an apparition of Splinter, overcomes his physical and mental wounds. They eventually return to New York City with the goal of finding Splinter, Karai, Kirby, and their other missing allies and liberate the city from the Kraang. They are successful in finding Splinter and set up a temporary base in the abandoned Antonio's Pizza, and Donatello begins work on new samples of retro-mutagen as the search for Kirby and Karai continues.
Meanwhile, Shredder sends his new minions Bebop and Rocksteady to find Karai. The duo succeed, and Shredder promises to cure her. The turtles run into a new team called the Mighty Mutanimals, with whom they manage to banish the Kraang back to Dimension X and free New York. The effect of the invasion eventually earns Shredder cemented control of the city's criminal underworld for his efforts to create a mind-control serum meant for the turtles, Mutanimals and Karai.
The turtles are later offered by future time sorceress Renet to time travel to the past, where they meet up with a younger Hamato Yoshi and Oroku Saki, as well as Yoshi's late wife and Karai's mother, Teng Shen. During the battle between Yoshi and Saki inside the Hamato Clan dojo, Shen is accidentally killed by Saki, who meant to kill Yoshi instead. Saki leaves the dojo after his hair burns off from the fire and kidnaps Yoshi and Shen's baby daughter Miwa, vowing to raise her as Karai and leaving Yoshi to die. After his escape, the turtles save Yoshi before traveling back to the present with Renet.
When the Kraang return to Earth, the Turtles discover that the Kraang have another enemy from Dimension X in the form of the Triceraton empire. Despite their best efforts and Shredder violating the Foot Clan's temporary truce with the Turtles by stabbing Splinter during the fight, the ruthless Triceratons activate the Heart of Darkness, a black hole-creating machine which annihilates the Kraang, Earth, and everyone on it. But just as it comes to the worst for the Turtles, April, and Casey, they are rescued by the Fugitoid, an alien robot, and taken onto his spacecraft.
Season 4
After the Turtles, April, and Casey are saved from the destruction of Earth, the Fugitoid uses his spacecraft the Ulixes to travel six months back in time in order for him and the Turtles to prevent the Triceraton Empire led by Emperor Zanmoran from again assembling the three components of the Heart of Darkness that are scattered throughout the universe before everything on Earth is lost. Besides fighting the Triceratons, the Turtles also face new enemies in outer space like Lord Vringath Dregg of the planet Sectoid and the bounty hunter Armaggon, and even have an adventure with their interdimensional 1987 counterparts and their enemy Krang who is an exiled relative of Kraang Subprime. Despite the efforts of the Turtles, the Triceratons are still able to collect all three pieces of the Black Hole Generator, only for the Turtles to return to Earth and join forces with their past selves to warn Splinter before he is killed by the Shredder, stop the detonator of the Heart of Darkness, and defeat the Triceratons. The Fugitoid destroys the Black Hole Generator near the Triceraton spacefleet, causing to explode, presumably killing the Triceratons. In the aftermath of the fight against the Triceratons, the past versions of the Turtles, April, and Casey leave Earth with the past Fugitoid in the Ulixes while the present Fugitoid's head reactivates in Earth's orbit.
Weeks later following the Triceraton Invasion being thwarted and the Foot Clan's disappearance, April is promoted to kunoichi at the time when the witch Shinigami arrives and is revealed that she is Karai's friend as they plot to rebuild the Hamato Clan and dispose of Shredder who is still recuperating from his last fight with Splinter. While Karai and Shinigami got some ninjas on their side, the Foot Clan strengthens the Footbot army by creating the Elite Footbots. Furthermore, some other crime organizations have been plotting to take over the Foot Clan's territory and a crystal shard of unimaginable power which April received from the alien Aeons during their space adventure is beginning to exert a baleful influence on her. Using a special mutagen formula made by Baxter Stockman, Oroku Saki recuperates and becomes Super-Shredder to take back control of the Foot Clan. Once a stable formula is made, Super-Shredder attacks the Turtles, the Mighty Mutanimals, Karai, and Shinigami which ends with Splinter being killed in battle against Super-Shredder. This leads up to the final battle at Super-Shredder's hidden mansion, where Leonardo manages to kill Super-Shredder.
Season 5