Contain Soul

As an Action, the user can cast Contain Soul of a slain creature within 3 INT or Less. The Soul of the creature is put in a Stasis within the gem and is contained and invulnerable unless the Gem breaks. While in the Gem, the creature counts as being dead for as many seconds as it was before being put inside of the gem. If the creature is attempted to be brought back to life, it can only do so if the gem is within 5 feet of its original body. If a creature dispels the gem with Dispel Magic at Contain Soul's level, the soul is shunted out of the gem

The Caster can use an action to Release the Soul or release the soul by breaking the gem.
The Caster can use an action to cast Unseen Servant without a Spell Slot if a soul is contained within it, but must roll a D20 + their Spellcasting Modifier against their own Spell Save DC upon casting or the soul is released from the gem.

While the creatures soul is within the Gem, they are Incapacitated and invulnerable to all damage unless the gem is destroyed.