...Ahem. I have some news that I would like to share. I am going to be going around to inspect everybody to be sure. I am confident that this was an extreme circumstance... and is not something repeatable.
The world Bahamut came from is filled with distortions to the point where, when I tried to pull Bahamut away, I instead pulled from... a shell of Bahamut. A soulless body. I had never taken a spirit from there, only the memories of an empty body... and then, with my Voice-like attributes, formed a new life from it.
In other words, Bahamut, the one that you know, has memories that mirror the Bahamut of that world. However, he is not the same... and is technically a Cibus native. Or a Voidlands native, my Voidlands. And therefore, when everyone returns to their world... he will be staying with me, as well as the Void Eternas.
Do not be alarmed. I am confident that this is not the case for most, if not all of you. But I am checking to be sure.