She is a friend of the turtles, and currently a Kunoichi in training.
April O'Neil is voiced by Mae Whitman in the 2012 computer-animated series. The tomboyish daughter and only child of scientist Dr. Kirby O'Neil, April is sixteen years old; much younger than most other versions of the character who appeared as a young adult in her twenties. She likes to play video games and eat pizza. She is very gentle with animals, as shown in the episode "Monkey Brains." April lives with her aunt in the city and wants to be reunited with her father, who was captured by the Kraang. In "TCRI", it is revealed that the Kraang are after April as well. April befriends the Ninja Turtles after the Kraang kidnap her father, and Donatello develops a crush on her.
In "Monkey Brains," Splinter discerns that April has a natural spiritual sensitivity and offers to train her to be a kunoichi (a female ninja) so she may learn to harness her natural fighting abilities and defend herself. In "Baxter's Gambit", Splinter gives April a steel fan that was originally meant for his own daughter before the Shredder adopted her as this series' version of Karai. In "The Kraang Conspiracy", April's telepathic powers are revealed to be a by-product of her genetics: she is in fact a half-human/half-Kraang hybrid. In "The Lonely Mutation of Baxter Stockman" it is revealed that she is immune to mutagen; due to her half-Kraang nature.
During the second season, April has a falling out with the Turtles after a scuffle with the Kraang results in the accidental mutation of her father. She begins to tutor Casey Jones in trigonometry so he can stay on the hockey team. Casey takes to April immediately and calls her "Red". After the pair is saved by the Turtles twice, April decides to forgive the turtles and repair her friendship with them, culminating in Donatello managing to perfect a small sample of retro-mutagen that is used to cure her father, Kirby, and return him to normal.
When the Kraang had mounted a massively full-scale invasion on New York City, resulting in the Turtles being forced to retreat after Leonardo is badly injured and Splinter is lost in a sewer, April takes the Turtles and Casey to her old family farmhouse to recuperate. During this time, which took four whole months, they had encountered a Kraang duplicate of April's long-lost mother that tried to gain her trust and love so that it could abduct her and take her to the Kraang. The Kraang-human hybrid was later overpowered by a terrified April's inherent and unusually strong psionic abilities. At one point, she capable of levitating several cards in midair telekinetically. Later, when the turtles' were trapped within their own nightmares, April had utilized her exceptional telepathic abilities to wake them up. Upon returning to New York, April had used her stronger telepathy to restore Splinter's human mind and memories of his former life as Hamato Yoshi.
After her father, Kirby, was saved from Dimension X and reverted to normal again, she happily hugged him. Later, she and her dad went to help the people of New York City recuperate from the Kraang's invasion by passing out warm soup. Before the Kraang were all transported back to their home world of Dimension X, April assisted in fixing up the turtles' dilapidated home in the Manhattan sewers.
- The motto of April's school appears on a sign outside the building and on the floor in front of the entry. It reads "Aut disce aut discede", which is Latin for "Either learn or leave."
- In New Friend, Old Enemy The friending site which April showed Mikey is called "My Face, so-so social" - which is a reference towards Facebook by both name and overall layout and MySpace.
She can see through the eyes of another being.
Immune to Kraang Mutagen.