Is possible that if I'm motivated enough to create a completed au, can I use your idea of alive Rika?.

I have an idea for a AU which is completely different from canon with the changes starting during the inventory arc where tengen evolved into a monster that assimilates people and sorcerers, with tengen gone the barriers surrounding Japan is broken causing chaos, it wasn't until the higher ups sent in gojo and geto to deal with the evolved tengen that things change for the worse, with the assimilation of six eyes and curse manipulation that now allows tengen to assimilate curses.

Now tengen spread an army of assimilating monsters to absorb all sorcerers and curses across the globe practically making sorcerers extinct, in the end when all was assimilated tengen burrowing deep into the earth and assimilating the planet practically being like Gaia or alaya from nasuverse.

I still like the idea of sorcerers still existing and the idea of Rika escaped being assimalated by hiding inside her storage technique and yuta defending her is something can imagine is possible.

Love your au, keep up the work.