So slight spoilers for Cour 2 of the TYBW and the manga.

But Sajin, rather than being completely abandoned after his lieutenant originally picks him up, is sighted again after Yhwach goes up to the Royal Palace in the anime. While certain scenes have been cut out that lead nowhere, Sajins role post fight with Bambi has seemingly been expanded upon and given a bit more focus for some reason. Why?

There's obviously an idea that something is going to happen, and I just now had a brain bubble tell me what could happen. In the final battle with Yhwach the quincy king manages to shatter Tensa Zangetsu with the Almighty, only for it to be undone by Tsukishima's Book of the End, paving the path for our protagonists to win the day.

So, why do I bring this up? Well, seeing as we know entirely new fights are on the table both big and small (Ichigo vs Bambi's, Byakuya vs 3 Sternritter, the squad 0 battles from episode 25 and 26) and we already know to expect new scenes for the likes of Ukitake (Who very well could be getting a bankai reveal hopefully) and a new anime only scene is almost assured between Uryu and Ichigo.

So, what if what we're building up to is a new way to kill Yhwach? What if Tsukishima is gonna get the chance to use Book of the End on Sajin and Tensa Zangetsu, reverting Sajin to his human form to do battle against Yhwach alongside Aizen and Ichigo. We already know his power is very much unnatural so perhaps the Jinka Technique Sajin will help put pressure on Yhwach and even make him vulnerable, replacing the still silver arrow to help give Ichigo the opening to kill Yhwach while also giving him a more satisfying conclusion for sacrificing himself and not giving him quite such a harsh punishment. (Uryu potentially simply being in the fight from the get go as well.)

I know it's probably not likely that this is exactly what's going to happen, but it does feel like something is being built up for Sajin and I think this would be an amazing send-off for him.