Riddle Of The Ancient Aeons: Za-Naron was one of the seven elder aeons (the first seven aeons to exist) but after a meleniea their physical bodies disintegrated, so there souls were placed inside the Aeon Sol Star in order to exist forever. After April and her friends saved the planet Xaava-Dal by restoring the Sol Star, the lead Aeon takes a small piece of the Sol Star and gives it to April, saying that it will bring them luck and great power as well.
Over time as April continued to use the Aeon crystal to help her with her powers, Za-Naron started to slowly take control over April's mind and spirit, causing her to become addicted to the crystal, much to the worry of her friends. Eventually April became so addicted to the crystal that she refused to take it off even when the others told her she should.
The Power Inside Her: When Donatello tried to test April's psychic powers suddenly goes crazy, clutches her crystal tightly, and causes much of Donnie's lab equipment to be levitated and thrown around the room. Leo realizes this was a bad idea to begin with, before April glowers at him, then unleashes a psychic blast that sends Leo, Donnie, and the equipment flying away. When Raph, Michelangelo and Splinter enter and see what has happened, they carry her to the dojo to be treated with the healing mantras, yet the crystal seems to levitate towards her as she is carried out. When April wakes up she begins to panic as she realizes her crystal is missing. Splinter tries to hold her back and reason with her, warning her that she needs to break its hold on her, but April simply lifts him into the air with her psychic powers, and attempts to crush him. At the same time, her crystal is able to reunite with her, despite Donnie's best efforts. Once it reunites with April, Donnie she begins to choke Donnie psychically. Splinter shouts for April to fight the evil influence controlling her, but April fears it is too powerful for her to overcome before it asserts control again and subdues them both.
Afterwords Za-Naron looks down on NYC, gloating at all the people below, April tries to fight the evil influence, but it wants to purge the city of all evil. April seems to agree with it, wanting to destroy the evil to save everyone. While Casey Jones was battling the Foot clan, April defended aeon them and swiftly defeated Shredders henchmen. When Leo, Raph and Mikey arrive April is given control again but has no memory of what happened and before they can talk to her, Za-Naron takes control again and she leaves their presence. When they chase April to the top of the channel 6 Za-Naron reveals who she is and that she wants to purge the Earth of all corruption. When they try to stop her she flings the Turtles and Casey off the roof but Donnie then arrives and tries to reach through to April himself but April can't fight off Za-Naron's influence. After apologizing to Donnie, April lets Za-Naron retake control, and fed up with Donnie's attempts to help April fight off her influence, Za-Naron lifts Donnie up in her grip, and reduces him to atoms for his interference, much to the shock and horror of Donnie's brothers and Casey. After leaving the scene and crashing onto a rooftop in exhaustion, she begins to suffer guilt over what she's done but Za-Naron regains control and tells her she made her choice by picking the crystal over the Turtles and Casey, and tells her to let go of her connection to them and aid Za-Naron with purging the Earth of its corruption, starting with NYC.
Za-Naron then attacks the Purple Dragons. When the turtles and Casey arrive Leo tries to reason with Za-Naron again, but she warns them to stay out of her way, or she'll cleanse them as she did Donnie. Casey fears that they can't attack Za-Naron if April is still in there somewhere, but the Leo and Raph agree that after what happened to Donnie, April is gone, and they must take her down, leaving Casey devastated. When Za-Naron bests them they try and reach April, reminding her of everything they've been through together. Despite their best attempts to reach April, Za-Naron refuses to let April resurface, blasts them all away, and after tossing Casey aside when he tries to protect Raph, she prepares to cleanse him as well, but as Raphael begins to feel himself being ripped apart on the molecular level, he tries one last time to reach April by reminding her of Donnie. As visions of Donnie, along with her guilt of murdering him flash through her mind, April is able to regain control, stop Za-Naron from murdering Raph as well, and restrain Za-Naron long enough for Leo and Mikey to recover and Leonardo to tell her that she's the only one with the power to destroy the Aeon crystal once and for all. After resisting Za-Naron for a short time, April tears the Aeon crystal from her neck, and throws the crystal to the pavement, shattering it. However, this results in Za-Naron being exorcised from April's body now that her link to April was destroyed, and reassuming a physical form as the Aeons' corrupt form seen on Xaava-Dal. Furious that April chose her friends, family, and humanity over having all the power in the universe, Za-Naron charges her in retaliation, but furious over what Za-Naron put her through, April draws her tango blade and slays Za-Naron once and for all, ripping her physical form to shreds, and leaving Za-Naron's energy to disperse.