Is it possible to destroy a soul?

Question

Is there any method for a creature to destroy a soul, such that it is utterly wiped from the multiverse? No afterlife, no wall of the faithless etc etc

I was thinking about the nature of the multiverse and afterlives and it occurred to me that having an eternal soul is possibly one of the worst fates possible.

When gods die what happens to souls that exist in their heavens, hells, planes etc?

I guess their either swooped up by whichever god killed them, left to rot in the corpse of a dead deity or float around the astral sea until they eventually reach the fugue plane and join the wall / go insane.

So one could probably say there is a good chance that every soul that ever lived will eventually be abandoned / end up on the wall. And likely in between that time their souls will be juggled around by random gods being put in whatever heaven or hells in between.

If my character realised such an eventuality, or at least believed in it, what method could they take to ensure the destruction of their soul?

Answer 1

Get a barghest to eat you¹

This is probably the easiest solution, since barghest will attempt to consume goblinoid leaders. Simply pose as one using a spell like alter self and you can easily attract the attention of a barghest.

The section on the barghest in Volo's Guide to Monsters (p. 123) states

Soul Feeding

A barghest can feed on the corpse of a humanoid that it killed that has been dead for less than 10 minutes, devouring both flesh and soul in doing so...

Once a creature’s soul is digested,... no mortal magic can return that humanoid to life.

^{1: credit to guildsbounty for the mention in the comments}

Ask a lich if (s)he'll consume your soul for you

The section on the lich in the Monster Manual (p. 203) states:

Soul Sacrifices. A lich must periodically feed souls to its phylactery to sustain the magic preserving its body and consciousness. It does this using the imprisonment spell. Instead of choosing one of the normal options of the spell, the lich uses the spell to magically trap the target’s body and soul inside its phylactery. [...] A creature imprisoned in the phylactery for 24 hours is consumed and destroyed utterly, whereupon nothing short of divine intervention can restore it to life.

While Divine Intervention could still save you in either of the above cases, the options below can circumvent such restorative power.

A consumed soul coin

Another option that is tackled in Baldur's Gate: Descent into Avernus is the use of soul coins:

Each coin ... is inscribed with Infernal writing and a spell that magically binds a single soul to the coin.

Using this magic item to fuel an Infernal War Machine (also a feature of the same module) yields this effect:

If [the soul from the coin is] still trapped in the furnace when this duration ends, the soul is destroyed. Not even divine intervention can restore a soul destroyed in this manner.

The typical options

The 9th level wish spell can do almost anything with GM permission:

You might be able to achieve something beyond the scope of the above examples. State your wish to the DM as precisely as possible. The DM has great latitude in ruling what occurs in such an instance, the greater the wish, the greater the likelihood that something goes wrong.

The cleric's Divine Intervention feature might work as well:

Imploring your deity's aid requires you to use your action. Describe the assistance you seek, and roll percentile dice. If you roll a number equal to or lower than your cleric level, your deity intervenes. The DM chooses the nature of the intervention

Answer 2

Get a Hexblade to turn them into a specter. Kill the specter. The MM seems clear on the subject and it’s a fun alternate use of the 6th LV Hexblade ability.

The Specter's lore entry (p. 109, MM) says:

When a ghost's unfinished business is completed, it can rest at last. No such rest or redemption awaits a specter. It is doomed to the Material Plane, its only end the oblivion that comes with the destruction of its soul.

Answer 3

I can speak mostly as far as the 3.5 edition is concerned. I wouldn't mention it had you not put the forgotten realms tag in this post. There's a material in Complete Warrior named Thinaun. Should you kill somebody using a weapon made of this material his/her soul is absorbed by the weapon. There are other ways to capture a soul, mostly spells, but the first step is taking hold of one.

Now, absorbed doesn't mean destroyed, which brings us to the Book Of Vile Darkness. This book has an interesting option when it comes to using souls. A spellcaster can use a soul stored in a receptacle to overcome spell resistance or to craft an item.

And I quote:

Using a soul in any way other than simply transferring it as barter consumes it completely, destroying it forever. Destroying a soul is an evil act of the blackest sort, even if the soul was evil itself.

Hope this helps.

Answer 4

Turn them into a genie, and kill the genie

The Genie's lore entry (p. 141, MM) says:

A genie is born when the soul of a sentient living creature melds with the primordial matter of an elemental plane. Only under rare circumstances does such an elemental-infused soul coalesce into a manifest form and create a genie.
A genie usually retains no connection to the soul that gave it form. [...]
When a genie perishes, it leaves nothing behind except what it was wearing or carrying, along with a small trace of its native element: a pile of dust, a gust of wind, a flash of fire and smoke, or a burst of water and foam.

So a genie is a soul coalesced into manifest form, and if it dies, it leaves nothing behind but a bit of dust, wind, etc. The soul is gone.

One way to turn another creature into a genie would be True Polymorph. I think that the rules did not foresee that in this case, like for the specter, the target would be a creature that is a manifested soul, and so the DM will have to adjudicate how other spells or effects that affect souls (for example the soul cage spell) interact with it.