The Cures discover what Shindoine has done to Kyousei Maruyama, after Rate becomes ill again. Shindoine reveals how she evolved herself using a Mega Part and can now create GigaByogens from living beings. The Cures attempt to fight the GigaByogen but are easily defeated, so Shindoine leaves to show King Byogen her new powers. During the brief respite, Nodoka, Chiyu, Hinata and Asumi regroup and find Kota in the Zoo, with Kota visibly shaken having witnessed his father turn into a monster. However, Nodoka reassures Kota the Pretty Cure will save his father. When Rate senses the return of the GigaByogen, the girls rush off to face it, but despite their best efforts they are unable to purify the monster with Healing Oasis. Determined not to give up, Nodoka rallies the other Cures and they engage the GigaByogen again. Their determination causes the power of all their elemental bottles to combine and create a new bottle. Rate combines all of their powers into one, forming the Healin' Good Arrow. The Cures use their new items to perform Final Healin' Good Shower to purify the GigaByogen and rescue Kyousei Maruyama.

King Byogen forces Daruizen to power up using Mega Parts; despite being reluctant to do so, Daruizen complies. Meanwhile, Nodoka is paid a visit by Dr. Hachisuka, who looked after her while she was sick. Nodoka introduces Dr. Hachisuka to her new friends and he is grateful that Nodoka is doing so well. At dinner, Dr. Hachisuka reveals he quit his job at the hospital after he failed to cure Nodoka. Nodoka becomes upset and asks Rabirin if she can reveal the existence of the Byogens, but Rabirin dissuades her. Dr. Hachisuka goes for a walk with Nodoka and explains he changed careers to become a researcher who studies new illnesses to find a cure, and that Nodoka's encouragement is the reason, making Nodoka feel better. The next day, Dr. Hachisuka leaves but not before he and Nodoka make a promise to see each other again. However, he comes across Daruizen who turns him into a GigaByogen. After Rate senses Dr. Hachisuka is in trouble, the girls transform and try to rescue him. During the fight Daruizen engages Cure Grace, asking her what benefit working for others gives, but Grace is able to push him back, before helping the others purify the GigaByogen. Afterwards Nodoka watches Dr. Hachisuka leave, reaffirming her promise to meet him again when she grows up and the Pretty Cures' resolve to protect the world against the Byogens.