2(Crossover)

An Au where Sanzu dies in one of the future timelines or in the past before the final timeline and reincarnates as one of the primordial demons in Tensura.

With this the options are: Sanzu becomes Jaune/Carrerra, Violet/Ultima or he is the 8th Primordial which would be known as Rose(pink) and depending on who summons him or name him he could keep his canon name(Sanzu or Haruchiyo) or another(it really depends on who ends up naming him).

Sanzu would probably be a loose cannon if it is the future him but a more controlable one if it is the past him so that would affect how his relationship with the other primordials and other beings would be like.

I'm not sure how his existence/change would make to the canon story but then again that is something the writer should choose as it depends in their choices of who Sanzu reincarnates as, how the passing of time affects him, his relationship with others and lastly who would be his 'master' & name giver.