Souls return to the Aetherial Sea when they die, where they are eventually cleansed of their memories to be reborn anew. I think my memories as Kiyomi got washed away while I was there.

[ It's what would make the most sense, if she really thinks about it (and she has). ]

When I die, Ardbert and I will be reborn together. I expect the person we become will be quite troublesome, always thirsting for adventure and unafraid to seek it out.