Well hello there, Raychbunni here.
I wanted to share some lore about the universe in which the story is set. I have plans for more stories set within this universe so if you like my style and this story this is handy knowledge.
So first up, what's an immortal? Well, they're just your average soul that receives a 'spark' within their lifetime. That spark gives birth to a System on their entrance into the void at death. A System is, as the FL said, like the soul and the void went and had a baby, it is forever linked with the soul and is also forever linked to the void, like a bridge. Enabling the Soul to retain memories from the life they received a spark and future lives they live out.
