K³ is a story (not a fanseries!) by Cure Shabon, largely inspired by the Nickelodeon sitcom Sam and Cat. It's mostly focused on the lives of the now-young adults Erika, Yayoi and Makoto, who now live together at a small apartment complex near Akihabara and experience normal everyday life with no more evil to battle. Characters from other Toei works, both animated and live-action, also make appearances.
After so many battles against evil, the Pretty Cure All-Stars can finally go on with their lives and relax, as there are no otherworldly evil forces let to beat. Shortly after graduating from college, Kurumi Erika leaves Kibougahana and moves to the Toudou apartment complex, where she plans to install a personal atelier, only to find out that she has to share her apartment with two of her Pretty Cure kōhais, budding mangaka Kise Yayoi and popular idol Kenzaki Makoto. Not that they mind it...
- Kurumi Erika
- Formerly known as Cure Marine of the Heartcatch Pretty Cures. Although she has grown to resemble her sister Momoka in terms of appearance, Erika is still the self-indulgent, self-entitled, optimistic blue hurricane she's always been, and is dedicated to her fashion designer profession more than ever before.
- Kise Yayoi
- Formerly known as Cure Peace of the Smile Pretty Cures. Still as soft-spoken and dilligent as always, Yayoi is currently working on having her Miracle Peace project published on a monthly manga magazine -- that is, if there's any willing to accept.
- Kenzaki Makoto
- Formerly known as Cure Sword of the Doki Doki Pretty Cures. After the defeat of King Selfish, Makoto chose to stay at Earth with her teammates, while continuing her idol career. In K³, she has become more used to Earth's customs, and due to having a more reserved personality than Erika and Yayoi, she acts as the trio's voice of reason.
- Makoto's fairy partner. As there are no more evil forces attacking Earth, she now spends most of her time in human form, acting not just as Makoto's manager but also as the trio's self-proclaimed legal guardian.
- Mr. Kikuchi (菊池さん Kikuchi-san)
- The friendly manager of the Daisy Hills apartment complex.
- Ryuho and Haruto
- Former Bronze Saints of the Dragon and Wolf constellations, respectively, they now live next door to the K³ trio's apartment, though Haruto doesn't seem to stay around as often due to the constant tours with his band, which, according to Makoto, has performed with her a few times before. Contrary to popular belief, they are not a gay couple -- Ryuho admitted that, even if he was indeed gay, he wouldn't pursue a relationship with Haruto, as Haruto, in his words, "is already in serious commitment with rock'n'roll".