Aether is one's living soul. When one gets right down to it people are just flesh sacks used to hold their aether. When one dies, their aether moves on/returns to the land/what have you.Â
You do not necessarily have to go with the gun being forged from the demon's soul, the demon could just have been the gun's original owner and gotten stuck in the weapon after it was killed. Another option is that it is not the gun itself that is possessed, but a materia embedded into the gun that contains the demon's memories and experiences. Point is, you have a lot of routes to go with for what you are trying to achieve, some just more involved than others. Yar. ^ ^
You do not necessarily have to go with the gun being forged from the demon's soul, the demon could just have been the gun's original owner and gotten stuck in the weapon after it was killed. Another option is that it is not the gun itself that is possessed, but a materia embedded into the gun that contains the demon's memories and experiences. Point is, you have a lot of routes to go with for what you are trying to achieve, some just more involved than others. Yar. ^ ^