race features:
Kiss of Death
Famously their most used form of assassination, succubi and incubi are capable of ripping out the soul of a living creature just by kissing them. For this signature style of killing, their evil acts are easily recognized by blood hunters, clerics and others who seek to destroy such beings. After devouring an individual's soul, it is transported to the Kingdom of Never where the succubus or incubus' master uses them as they please.
There is one way however to free a soul collected by a succubus or incubus. You have to kill the fiend that took the individual's soul and preform a ritual with their blood, attempting to trade with their archdevil master for something they desire more than the person's soul.
Shapeshifters
The work of succubi and incubi is not easy. If they murder an individual in broad daylight, they risk the chance of being discovered by a cleric or other holy person, dooming them to be chased after or even killed by their radiant power. As a safeguard against such situations succubi and incubi are gifted with the talent to shapeshift.
Some turn into shadowy figures, assassinating their targets and taking their soul as their last breath escapes their mouth.
Others shift into the desired form of a curvy woman, a muscular man or sometimes into their target's significant other to charm and deceive, leaving them vulnerable and defenseless at night or in their own homes.
Mistaken Desire
Folktales and bards' songs tell tales of succubi and incubi falling in love with a certain individual and even bearing children with them, however this is an extremely rare occasion. These devils usually do not feel emotions, nor do they have the desires a human or other intelligent race would. They are born to fulfill only one goal: serve their archdevil creator. Some folk mistake their decade-long missions for love or attraction, however most of the time this is only a means to an end for them.
Rarely however, succubi and incubi are born with emotions and feelings like any other race. When in pursuit of a person they might meet their soulmate and fall in real, humanly love with them. This is a dangerous game for them because if their archdevil finds out there is only one way for them to survive: kissing their one true love without taking their soul. If they are capable of such an act, their bond to the Kingdom of Never is broken, their creator has no domain over them anymore and they lose their natural hunger for souls.
Soul Collector
Utmost value to devilkind, succubi and incubi work to collect the essence of the living. Their archdevil masters send them to the Material Plane to fulfill a mortal's end of the bargain, taking their soul whole or on rare occasion only part of it. If they are tasked to find a certain individual, they fight to the death to acquire their spirit. These fiends are capable of living with or stalking a person for decades if needed before they strike where their target is most vulnerable.