April's Aeon Crystal was a small crystal fragment of the Aeons' Soul Star that was given to April O'Neil as a reward for saving their planet in the episode Riddle of The Ancient Aeons. According to Donatello, the crystal has properties not found on Earth.
When both the Turtles and the Triceratons came to Xaava-Dal in search of the first piece of the Black Hole Generator, the corrupted Aeons attacked both sides. As the Triceratons got away with the fragment, April finds the Soul Star and returns it to its rightful place atop the pyramid, restoring the Aeons and their world to their pure form. In gratitude, the Aeons give April a piece of the Soul Star to provide her with luck and power.
As the Turtles and Fugitoid get captured by the Triceratons. Casey and April had to get back the first piece of the Black Hole Generator. She uses her crystal from the Aeons to open the doors of the armory where the piece was. After escaping from the Triceraton Mother Ship, April uses the crystal to summon the stealth ship and the group escapes.
After the defeat of The Triceratons, The Kraang and Shredder. April keeps the crystal as a necklace and she becomes a full Kunoichi. When she finds Karai and Shinigami (who stole her Dragon Tanto) she wants to know what's happening before the Turtles arrive. April uses the crystal to conform Karai is telling the truth about being on their side and her plans to rebuild the Foot Clan. April fights Shinigami to get her tanto back but during the battle, April's rage is amplified due to the crystal and causes her to start firing powerful psychic blasts around Shredder's old lair but Shinigami is ordered by Karai to give the Tanto back. Even the battle was over, April was starting drawing her Tanto due to the rage being amplified by the crystal but Donnie calms her down.
April uses her Aeon crystal to find Baxter Stockman and his henchmen as tracking mutants is easily than tracking humans. She is able to track Stockman to Shredder's old lair where Karai was being attacked by the bugs.
April starts to become very possessive of her crystal from The Aeons that she doesn't allow Donatello to analyze it but she agrees. April took the crystal to help her friends fight Monoculus that was brought to life. Donatello gets shocked seeing April with her crystal. April says its hers she needs it. She uses the crystal to control her tessen and destroys Monoculus. She gives back the crystal to Donnie so he could analyze it a little more. Mikey, who was convinced that the crystal brings comic book characters to life, steals it from Donnie's lab and the crystal makes Wingnut and Screwloose come to life. When Mikey shows the crystal to his favourite heroes, they steal it and become more-animalistic. After knowing what happened, April is furious at Mikey for taking her crystal without permission. The team fight Wingnut and Screwloose in the church tower and upon seeing Wingnut wearing her crystal, April starts launching thrash balls that hit Wingnut and the bell causing it to ring. Mikey uses that to make Wingnut and Screwloose suffer from the ultrasonic noise and April uses her psychic powers to retrieve back the crystal. After making Wingnut and Screwloose go back to his comic book world, April refuses to let Donnie analyze it more and says anyone or anything takes her crystal ever again.
Donnie tries to test April's psychic powers and causes a huge explosion that put April unconcious. The Aeon crystal wants to go back to April but Raph manages to hold it for a while. As Donnie tests the crystal, it goes back to April now that she awake and an evil influence takes control over April. When Casey was in trouble when he was stopping Shredder's goons from giving Shredder more mutagen. April appears to save him and takes out all the three out with psychic powers. She goes away to Channel 6 building and April struggles more into not allowing the evil influence take over her but she isn't strong enough and the evil influence (Za-Naron) makes her to make Donatello disappear. When April escapes and regains councious, she's so sad that she killed one of her best friends but Za-Naron takes her over again and says the crystal can help her break the connection with her friends. The Turtles and Casey try to make her destroy the crystal and after some struggling, April takes off the crystal from her neck and throws it to the floor with a furious yell, destroying it. Za-Naron leaves April's body and materializes to her form, angry of April choosing her family instead of all the power of the universe, charges at her but April draws her tanto blade and destroys the creature cutting it in half. When April is devastated that Donnie is gone because of her, she sees the rests of her Aeon crystal and figures out that Donnie isn't gone completely, that his moleucles were only scattered, she concentrates the broken pieces and is able to make Donatello's molecules restore him to his normal form.
Effect on April
The Crystal is shown to amplify April's budding psychic powers, to the point where it can give her telekinesis. She has used this ability to direct her tessen in flight, and to repel enemies and objects directed at her and her allies.
When Donnie tried to study it, a strange spectral mass came out of the Crystal, bringing several pieces of equipment to life. Later it shown to bring Monoculus, Wingnut, Screwloose, and their gear from a comic book to life.
This crystal is not without flaws. During Bat in the Belfry, April was complaining about headaches and strange nightmares about outer space. However the most noteworthy drawback about the Aeon Crystal is its addictive properties. April became overly obsessed with this relic, quickly snapping at the Turtles, and straight out calling it hers. Even Wingnut and Screwloose weren't immune to its properties, as Wingnut stated the crystal was the source of power and life itself.
The Crystal itself looks like the tip of a spear or arrow, welled out in the middle of the diamond-shaped head. On the opposite side of where it connects to the necklace, it has a small hollowed-out circle.