there are 3 total endings -
Find 0 souls you get the message "I don't know what happened. In my journey back down, I forgot my soul and with it, the recollection of my past life."
Find 1-4 souls you get the message "There was a war, I remember, It destroyed humanity, but how did all of this happen. My soul is incomplete, I need more of it to further recollect."
Find all 5 (not 6, idk how you found 6 that shouldn't be possible) and you get the message "My complete soul of my past life tells me that there was a war. Atom bombs destroyed the world, and all that were left standing were sent to Hell."
At the end of all, you get sent to hell with everyone else.