Ideas on handling a Magical Girl-fantasy book with subtle, dark undertones and themes?

I'm working on a magical girl story at the moment and want to strike a balance between two very different tones. On one hand, I want it to be a book full of bubbly, colorful aesthetics, themes of friendship, magic, and also featuring various epic magical transformation scenes (or at least as epic as it can be in writing). Just an overall a fantasy-girly vibe.

On the other hand, I also want to explore darker undertones and real, heavy topics like trauma, loss, or identity. The idea being that every main character—seven in total—has a deep arc they're going through or some kind of personal issue that would be resolved and/or explored in a meaningful way. The world itself would also have subtle disturbing elements in it's history that would be discovered over the course of the story (another idea of my story, that even a colorful fantasy world like this isnt the utopia it always looks to be on the surface).

I've naturally tried blending the tones but no matter how I write it it always feels... inconsistent to me.

My challenge is figuring out how to blend these elements without making the tone feel messy or jarring. I want to balance both tones without letting one overpower the other or making the contrast feel inconsistent.

I have tried writing scenes that start off lighthearted, only to gradually reveal deeper emotional layers in the narrative and the characters' past—but in all honesty I’m not sure if the shift feels too abrupt or forced.

I have also tried a few different approaches to blending the tones—like switching to the villains' POV or using dream/nightmare sequences to introduce darker elements, but I'm still experimenting with what feels right.