Succubi are known to mate with countless mortals, and in your case the offspring of such a union has diluted the bloodline as eons passed. For many this heritage reveals nothing. For some, this blood results in some random element of Daemonic power being born centuries down the line. In even rarer times, it becomes significant, or awakened enough, to manifest in arcane power.
Fiendish Ancestry
At 1st level, you can speak, read, and write Infernal. Additionally, you bear some mark that Daemons can see or sense that renders you different than other mortals. Daemons do not automatically attack you or are automatically hostile to you, treating you as they might another fiend. Finally, whenever you make a Charisma check when interacting with fiends, your proficiency bonus is doubled if it applies to the check, if it wasn't already.
Profound Appearance
Also 1st level, your form is transformed through your bloodline to that of the epitome of an attractive creature of your race and sex. Humanoids in particular find your form simultaneously distracting and alluring, particularly in combat. When a humanoid creature is targeting you with an attack, they cannot treat your armour class lower than your Charisma score. As a bonus action or reaction to being targeted by an attack, you may apply this armour class to all creatures that attempt to attack you for 1 minute.
Once you use this feature you cannot do so again until you finish a long rest.
Become Heritage
Starting at 6th level, you can channel your sorcerous power to become what is deep within your bloodline. By expending at least 1 sorcery point as a bonus action, you become a half-Succubus, losing all of your statistics and class features, but retaining your alignment and personality. You gain the statistics of a Succubus.
This transformation lasts 1 round per sorcery point expended, ending at the beginning of your turn when the effect expires. You may, as a bonus action, revert to your normal form but must expend additional sorcery points to transform again. Any creature dominated by the charm feature of a Succubus becomes free from that enchantment when you revert to your normal form. Whenever you change forms, you retain any damage you've succumbed to in either form. If you die while in your succubus form, you revert to your normal form.
At 8th level, this transformation lasts for 1 minute per sorcery point expended. At 10th level, it lasts for 1 hour per sorcery point expended.
Duplicitous Persona
At 14th level, the talents flowing through you enhance your capabilities in social interaction. You gain proficiency in Deception and Persuasion. If you already had proficiency in these skills, you gain expertise in them.
Mortal Fiend
Beginning at 18th level, your dual nature of Daemon and humanoid mortal has become intertwined. Your type is Daemonic for all purposes of abilities, spells, and magical effects, even when you are not transformed into a Succubus. Your type is also still a humanoid. Because of this, you stop aging, you do not need to breathe, sleep, drink, or eat, although you do need at least 4 hours of quiet meditation to finish a long rest.
Through this fiendish shift, your Charisma score increases by 4 to a maximum of 24.