Reaper

Reapers use the power of souls to grant themselves offensive and defensive powers. They get stronger which each soul they collect. They store souls in their weapon and expend those souls to gain power.

3rd: Soul Trap

Choose a weapon that you are proficient with, that weapon becomes a vessel for storing souls. It can store up to 6 souls. At the end of a long rest, if you have less then 3 souls, you gain souls until you have 3 stored. Each time you kill a creature with the weapon, you can store a soul. For every two souls you have stored in the weapon, your attacks deal an additional +1 damage (max +3). 

When you hit a creature with that weapon, you can expend a soul to force the creature to make a wisdom save or become frightened of you. The saving throw dc is equal to 8 + your constitution modifier + your proficiency bonus.

3rd: Soul Sight

Your eyes awaken, granting you the ability to see creatures souls. Souls appear differently to you based on the type of creature:

• Aberrations: Dark purple
• Beasts: White
• Celestials: Gold
• Dragons: Platinum (good) or Crimson (evil)
• Elementals: Fiery red (fire), flowing blue (water), swirling white (air), and rambling brown (earth)
• Fey: Pink
• Fiends: Pitch Black
• Giants: Gray
• Humanoids: Blue (colors change according to emotions, perhaps yellow when happy or red while angry)
• Monstrosities: Orange
• Plants: Green
• Constructs: If the construct has a soul, it appears light gray
• Undead: If the undead has a soul, it appears wispy black

This sight extends 15 feet from you. When a creatures soul is visible to you, you roll insight checks at advantage against them.

7th: Indentured Soul

Once per rest, you can use a bonus action to release a soul to fight for you. It takes its action immediately after yours. The soul takes the form of a humanoid with the statistics of a cult fanatic. The spirit has the following changes to to its statistics:

• No spellcasting
• Gains a bonus to attack rolls equal to your proficiency bonus
• Armor class of 15
• Deals force damage with its attacks
• Cannot be grappled, stunned, paralyzed, restrained, or petrified
• Resistant to non-magical attacks
• Cannot regain any hit points
• Maximum hit points equal half your maximum hit points

The spirit lasts for one minute or until it drops below one hit point.

10th: Purgatory

When a creature dies, its soul is waiting in purgatory. When you kill a creature with your soul trap weapon, you can exchange its soul for a soul in purgatory. 

When you kill a creature with your soul weapon, you can cause a creature who is making death saves within your line of sight to regain hit points equal to the damage dealt by the killing blow, or you can cause a creature who has died within the past 10 minutes to regain hit points equal to the damage dealt by the killing blow.

When you drop below 1 hit point, you can expend one of your souls and a hit die to remain standing with hit points equal to a roll on your die.

15th: Advanced Soul Sight

Your soul sight now extends 30 feet from you. You gain the following additional benefits from your soul sight:

• Creatures cannot benefit from invisibility against you while within your soul sight
• You can see souls through darkness and magical darkness. They glow 5 feet of dim light in all directions that only you can see
• You cannot attack at disadvantage against a creature when their soul is visible
• Your soul sight extends into the ethereal plane while you are on the material plane

18th: Soul Barrier

As a bonus action, you can release any number of souls. For each soul that you released, that soul whirls around you. Each time you would take damage, one of those souls jumps in front of you, granting you immunity to the damage from the attack and all other effects from the attack. The soul dissipates after doing so. The souls last for one minute or until all the souls are expended. At the end of the minute, any remaining souls return to your weapon. You can only use this feature once per long rest.