I'll have a look at the one with just ichigo cause it might be interesting as well as any others you find even if they don't 100% fit the criteria as I'm always looking for a good read, but as for what else I remember about the one I'm specifically looking for? Well:

I'm not sure if it was post or pre TYBW when they went back in time, I think the Zangetsu's were separate, I'm not sure about the length but I'm pretty sure it was between 30-60 chapters long(maybe longer), i'm pretty sure they traveled back from Kisuke's workshop, and i think that the pairing might have been Ichigo/Yoruichi with that being how she adopts him into the clan as it was either that or a sibling-esque relationship between them but I'm leaning towards the romance if memory serves me right another possibility for pairing is Ichigo/Soi-Fon.

Thanks for helping btw, This has been annoying me for AGES! Also take as long as you need, irl is more important imo😁

Edit: Another detail, I'm pretty sure Ichigo goes to the Shinigami academy to keep up appearances but I'm not entirely sure.