Looking for fantasy recs where the MMC has a younger sister who actually matters to the story.

I’d love a series where the MMC is close with his younger sister who have lots of scenes together, a solid role in the plot, and is protective of her
– Preferably adult fantasy over YA.
– I’m not super into that classic YA/prosey/older-style fantasy writing. I struggle with it (probably because I’ve only now started to read books so I’m used to all the popular booktok ones) so I’m looking for new-ish books or ones with a really easy, modern writing style.
– I’m also open to books where they’re not blood siblings but still have that deep, platonic, soul-level bond like very emotionally intimate but strictly friendship.

For context, I recently read the first book of The Lady of Darkness series by Melissa K. Roehrich, and the platonic connection between Cassius and Scarlett is exactly the kind of dynamic I’m craving. If you’ve read it or understand what I’m looking for and know anything similar, I’d love recommendations.