Dayu (formerly known as Dalia) is one of Master Xandred's two followers, a female figure with a shamisen. Before becoming a Nighlok, she was a newlywed to Deker. But when a fire (implying to have been set up purposely by Serrator) burned their house down and injured Deker leaving him with moments left to live. A mysterious Nighlok appeared (later revealed to be Serrator) who offered Deker's life back in exchange for her humanity. When she accepted the deal, Deker indeed lived on but as half-human, half-Nighlok with no memory of Dayu. Dayu then became a Nighlok herself with only her shamisen (which was once her decorative lute) by her side to remind her of her past. Of all the villains, Dayu is the only one who cannot let go of her past once making an attempt to reclaim it by kidnapping brides and using their tears to create a wedding dress. Her plan failed due to the Rangers' interference, though she is saved by Deker. She is a powerful fighter as she took down both Kevin and Mia at once. Her shamisen (which she calls her "Harmonium") has a hidden short sword in the neck which she uses for battle. She has a habit throwing the baki of her instrument at Nighloks' she gets angry at. In "Broken Dreams," Master Xandred was getting tired of Dayu's failure and breaks her shamisen causing her to go to the human world and fix it with a musician. Mia pursues Dayu only for them to be put under a sleeping spell by Rhinosnorus. Mia witnesses Dayu's past in a nightmare. After the sleeping spell wore off, Dayu attacked Mia (who wanted to help Dayu after what she saw) only to retreat when Emily arrived. In "The Ultimate Duel," Dayu meets with Deker before his duel with Jayden. Around the time when the Black Box was completed as seen in "Super Samurai," Dayu abandons Master Xandred and Octoroo and goes into the human world. In "Trading Spaces," Dayu meets with an outcasted Furry Wart on a river stream where she plans to find a way to end Master Xandred's life for casting her out and breaking her harmonium.
In "Kevin's Choice," Dayu finds the part of Deker's sword and is approached by Serrator who offers to fix Dayu's harmonium in exchange for the info on where Deker is. While the two talked, it was revealed Serrator was the one who turned Deker into a half-human/half-Nighlok. Dayu is wondering if Serrator is lying until she finds Deker in the forest. Dayu learns from Deker that his sword Uramasa had taken the blow in the fight against Jayden. She and Deker crash the battle between the Power Rangers and Scarf where they attack Scarf in order to unleash Skarf's true power.
In "A Sticky Situation," Dayu receives a special dagger from Serrator.
In "The Master Returns," Dayu states her unhappiness with how long Serrator is taking to fix her Harmonium. Soon after Serrator heads to a cliff, Dayu senses her Harmonium presence and heads after Serrator. After she manages to catch up with Serrator, she fights him only to be knocked down by Serrator. After Master Xandred returns to Earth, he fixes Dayu's Harmonium and Dayu swears her loyalty once again to Master Xandred.
In "A Stroke of Fate," Dayu tries to convince Deker not to trust Serrator and Antonio begs him to reconsider his role in the battle between Humans and Nighloks following him remembering his past memories. Yet Dayu was unable to convince Deker to not trust Serrator.
In "Fight Fire with Fire," Dayu returns to Master Xandred's ship and speaks with Octoroo a plan to ambush the Power Ranger. Dayu and Octoroo send Fiera to help take down the Red Ranger. Dayu and Octoroo were surprised that the Fire Flashers didn't fully consume Jayden and suspect that Jayden isn't the head of the Shiba Clan.
In "Evil Reborn," Dayu senses the fight between Deker and Jayden. Dayu then senses that Deker is gone as Octoroo tells her to play her Harmonium to help recharge Master Xandred. Dayu declares that her Nighlok fate is sealed and that she has nothing left to lose as she unleashes the Moogers and some giant Moogers on the marina. Dayu then plays the Harmonium as Mia confronts her. Mia ends up slashing Dayu and her Harmonium where the Harmonium's destruction ends up unleashing a lot of misery which is enough to restore Master Xandred. Dayu then tells Master Xandred that she always pays her debts.
In "The Sealing Symbol," Dayu collapses Master Xandred stating that she played it for Deker and that it was the end of his sadness. Dayu stated that she wasn't truly a Nighlok. Master Xandred puts Dayu out of her misery as he absorbs Dayu's human half to serve as his defense against the Sealing Symbol and keep him from drying out though xandred was destroyed anyway.