The Souls mod is an inventory storage mod that holds your items in an enemy mob (soul) that you have to fight in order to reclaim your items.
Once you die, the soul will be in the exact spot you died. So you’ll have to trek back to your place of death and confront it.
It’s a non-hostile mob until you start attacking it and once you do it won’t stop attacking you until you are dead again.
But if you should succeed in defeating the soul it will drop all of the items you had pre-death.