Dead Soul

As a half born... You have a fondamental understanding of the mécanism of life. You sometime feel closer to death, and the sweet touch of the dark weaver. Reanimated from the womb, cursed or the the born child of a lich, the origin of this grime connection is generaly a storie not to be told...

"Annabelle, not four hours ago you instructed a dead man to stand up and he did.”

“Okay, he wasn’t dead, obviously. He was almost dead, at best... But the treads was there ok!”

“No. He was dead, and what with all those treads your speaking of... “

“I felt his... pulse! It was very faint!”

“You called his pulse. No one else would have felt it, because it wasn’t there except in response to you.”

“What your not telling me!”

“So much Magnus...”

-Molly Hall, ofgeography.tumblr.com with some modification of my own

The dead art

Your link to the sewing of death allow you to know by born right what other will never wisper. You may learn any spell from the school of necromancy, and treat it as if it was a sorcerer spell. You must obey all other restrictions to spell choosing.

You can maintain control over a number of creatures equal to your proficiencies. If you animate another undead creature while already controlling the maximum number, the oldest creature you've created is immediately freed from your control and becomes hostile to you.

Animatheurgie

You can use your réaction to take soul from one creature that is being killed or spend 10 min as a rituel to absorbe the remnant souls fragments of a corps. when you do this, you recover hit points equal to your proficiency bonus, add a sorcery point to your sorcery points pool and roll a arcana check(10) to learn a fact that the person knew. 
Before you do a long rest, if you still have more then the normal max number of sorcery points, you keep that number. 

On top of that, your knowledge of the soul help you make the best of yours sorcery points when use with the art of necromancy. When you use a meta magic with a spell or cantrip of the necromancy school, you can subtract 1 sorcery point from the cost of that metamagic (minimum cost for a metamagic is still 1 sorcery point).

Power of the soul

At 6th level you learn many ways to change and control the soul of other to some degree.

You learn to empower your undead servants. As an action, you may expend two sorcery points to infuse a chosen undead with additional necrotic energy. For the next minute, the target creature inflict bane when he damage a target, gains temporary hitpoints equal to your sorcerer level, and deals an additional 1d4 necrotic damage on all melee attacks.

You also learn to bring a soul back to the body  of a past living. You may expend five sorcery points to cast revivify on a non-undead creature without using a spell slot or material components. Once you cast revivify in this way, you can't do so again until you finish a long rest.

In adition, you can spend 1 sorcery point and a bonus action to change the creature type of a target to undead for 1 minute.

Soul exposure

One time by long rest, you choose one creature you can see within 60 feet of you, expose its souls until the end of your next turn. The next time you or an ally of yours hits the expose creature with an attack, the creature has vulnerability to all of that attack's damage, and then you and/or the ally who made the attack regain hp equal to the damage, then the draining ends.

Dark aura