Mashiro is preparing to enter a picture book storytelling contest. While thinking of ideas at Sorashido Park, Monda approaches her again, but she notices that he is acting differently than before.
Shalala comes to Sorashido City to report the results of Tsubasa's research into Kira Kira Energy. While spending time with her, Sora confides in her about her struggles.
While working on her new picture book at Sorashido Park, Mashiro meets Monda again and shows him her work, only for him to get angry at her due to their differing opinions.
The Cures go to investigate a mysterious tunnel that has appeared in Skyland, where Empress Undergu, ruler of the Undergu Empire, appears and overwhelms them with her power.
Elleelain and Empress Undergu meet and attempt to establish peace between Skyland and the Underg Empire, but Skearhead and Emperor Undergu oppose them, believing that strength is everything.
As the Cures prepare for their battle against the Underg Empire, Skyland celebrates a Christmas event called Strichmas, and they plan a party to cheer everyone up.
Ellee encounters the Morning Star, which is revealed to be Princess Elleelain and gives her the power to age up into a teenager without having to transform into a Pretty Cure.
The Cures fight to protect Skyland from Empress Undergu. Just as they are about to convince her to stop fighting, Skearhead returns and impales her before retreating to the Underg Empire.
Skearhead uses Empress Undergu as bait to lure the Cures into the Underg Empire, where he reveals his true form as Darkhead and that he was responsible for murdering Emperor Undergu and manipulating Empress Undergu and her memories.
After rescuing Empress Undergu, the Cures face the final battle against Skearhead, who emerges from the Sea of Underg Energy having transformed into a giant snake named Daijarg and attacks Earth.