I never thought about it before up until I went to the Rising Stones and saw that the case that once contained Tupsimati is empty.

I watched the scene where Tupsimati was used to defeat Nabriales, but scenes after that it pretty much was never seen again.

It's been a while and I don't know if there were any npc dialogue saying that one of that it's being kept hidden away from the Asciens or that one of the Asciens stole it. But in terms of Inn cutscenes I don't see any mention of such.

So, what happened to it? It's quite an important artifact to simply be forgotten.