Have you given any thought to an AU where Shiki activated her powers but her connection to the Gojo clan wasn't known or obvious? Like she was raised by her mother with an unknown father and maybe hide or lack distinct Gojo features. I imagine Nanami would try to shield her from the sorcerer world but eventually need help in dealing with her abilities.
In a world where the Nanami grandparents are less kind and believe in conservative jujutsu ideals, Nanami Shizuka and Nanami Kento grow up acutely aware of the jujutsu world.
Shizuka was neither born with the ability to see cursed spirits nor cursed energy of any note. She still meets Gojo Arata, still falls in love -but in this world Shizuka is more timid and fearful thanks to her grandparents' upbringing, and Gojo Arata bows to the pressure exerted upon him by his sister to marry a suitable partner for the good of the Tobiume family.
So when Shizuka discovers that she's pregnant with Arata's child, she runs.
Years later as a first year student in the Tokyo jujutsu school, Nanami Kento finds his sister living in a rural village with a young daughter. A daughter who looks nothing like either of her parents, but looks strikingly like Gojo Satoru instead -minus the eyes.
Shizuka doesn't want her daughter to become a sorcerer. The Gojo hair color can be hidden using hair dye, and for a while it seems that all will be well-
And then an accident leaves Shizuka dead and Shiki with glowing blue eyes.
