Soul Knight

For most people they would kill something and leave it at that. A Soul Knight would see it as an opportunity to empower them by taking their soul and utilizing its power to aid them. Soul Knights can use the power of souls to guide them, empower their blow, or use the life force to heal themselves. They can even infuse the magical power of souls into weapons.

Soul Steal

You learn how to harvest souls from the recently deceased and by using the soul’s consciousness you allow the soul to guide your next attack. Starting at 3rd level whenever you kill a creature with a CR of at least 1/4 you gain a soul. As a bonus action you can use a soul to double your proficiency bonus on your next attack roll.

Soul Strike

Now that you are more experienced in the art of soul stealing you now have a new way of using souls. You can take some of the magical power within them to empower your blows. Starting at level 7 you can use a bonus action and two souls to make your next attack deal an extra 1d8+your fighter level necrotic damage.

Phantom Guidance

You can use your souls to help guide you when you need them. At level 10 you can use a bonus action and three souls to give yourself advantage on your next skill check or saving throw. 

Undead Aid

By tapping into the life force of souls you can add it to your own. Starting at level 15 you can use a bonus action and three souls to heal 1d10+your proficiency bonus. Any excess healing becomes temporary hitpoints.

Soul Blade

You have learned how to infuse the magical power of souls into your weapons giving them much stronger attacks. Once you reach level 18 you can use a bonus action and 10 souls to enchant a non magic weapon making it a magic weapon for 1 minute. The enchanted weapon deals an extra 2d6 necrotic damage.