If the show was rewritten differently, I can only think of two more characters to add to the story. There's already a fanfic named after this show by a writer, whose OC is portrayed as Senku's science partner, best friend, and girlfriend. Mine are Shunrล Seiji and Suiren Tsukishinju. They're also best friends of the writer's OC, Sumire Weinberg (neรฉ Maeda), and love interests of Asagiri Gen and Saionji Ukyo.
And each plotline and design (for the attires, of course) has the elements of Avatar: The Last Airbender, DreamWorks Dragons: RTTE and Winx Club, with a hint of the Bayonetta, Skylanders: Imaginators, and Identity V games added to it.
In this story, Seiji and Tsuki are the earthbender, waterbender, and (as an inspiration from the Bayonetta series) both weavebenders. Each girl has a chi that is sometimes reflective in their eyes and determines what element they represent. It also serves as a conduit when the energy flows with it, like their hair for instance. Even Sumire has her own element that differs from those those who are attuned to nature; the power of music. Like Homura, all three of the girls are gymnasts, and it's during the finals of the tournament when their powers are awakened by a new source; the Dragon Flame. After the petrification took place, they became separated from each other until waking up 3,700 years later, but are wearing in their new outfits except for Sumire, who has yet to discover her what her element is.
Whew, this is long. But I gave it my best. Let me know what you guys think and whatever I need to add.