Hi, a pleasure to speak with you
-You must be new to the series. In SC, succubi are demons of lust. Not waifus, not girlfriends or "misunderstood people". They are demons. Like the ones in the bible. Terrible creatures formed from the depths of The Scorching Hell after an evil spirit is attracted there to take form. Not soul though. Humans don't go to neither heaven nor hell when they die. Where they go is a mystery.
-The neutral woman is in fact a witch, not a succubus. That's why she's neutral. A witch is a woman that makes a pact with a succubus for knowledge and power.
-The only way a mortal girl is made into a succubus is to have sex with an incubus. I... don't know if you really want that. NTR is very unpopular around... everywhere really. There is already one scene in game showing how they are corrupted.