Soul

Soul is an arcane force that is generated from bugs and is the substance that animates their bodies. When put to use it can be twisted into Spells or even be used to heal damage.

In-game, SOUL is represented on the HUD by a circular meter that fills up with white liquid, revealing two eye holes and giving the meter the appearance of a face. The maximum amount of SOUL the SOUL meter can hold is 99. This amount shrinks to 66 when the Knight dies but goes back to normal when the Shade is killed.

Lore
Soul is a life-force which animates most creatures in Hallownest. It can also be found in the air itself. There are various ways to store Soul. The Ancient Civilisation which predates the kingdom of Hallownest created Soul Totems which are able to store Soul inside. It can also be stored in jar-like caches and inside Soul Vessels.

Soul can be used to power Spells, such as Vengeful Spirit, Desolate Dive, and Howling Wraiths, which were made by the Snail Shamans. When using Focus, Soul can be used to heal damage. Several Charms interact with Soul as well. The Kingsoul contains limitless Soul within, while Deep Focus draws in Soul from the surrounding air.

The Soul Sanctum's Scholars tried to use Soul as a means to repel the Infection. They became Infected regardless, and some were left with aching minds while hearing the whispering of the stolen Soul inside them. The misuse of Soul deformed other Scholars into Mistakes and Follies, making them lose their shape.

The Knight uses the same method the Scholars did for acquiring Soul: taking it from bugs which are still alive, and taking it from Soul Totems. It is also possible for the Knight to obtain Soul by striking enemies with the Dream Nail. Godseeker refers to the Knight as "eater of Soul".

Usage
SOUL is used to cast damage-dealing Spells or to Focus, which heals the Knight over time. When there is enough SOUL to cast a Spell, the meter flashes briefly accompanied by a soft sound effect.

Casting Spells or using Focus requires 33 SOUL. Using the Spell Twister Charm reduces the cost of casting Spells to 24.

Acquiring SOUL
There are several ways to acquire SOUL throughout the game:

Attacking Enemies

 * Enemies struck with the Nail cause the Knight to gain SOUL at a rate of 11 per hit.
 * Several Charms can modify this amount:
 * Soul Catcher increases the amount of SOUL gained to 14
 * Soul Eater increases the amount of SOUL gained to 19
 * The two above Charms stack, doubling the amount of SOUL gained to 22

Dream Nail

 * Striking enemies with the Dream Nail gives 33 SOUL. The Dream Wielder Charm doubles this amount to 66.

Soul Totems

 * Soul Totems are structures found throughout Hallownest. They glow with Soul energy when the Knight approaches. When hit with the Nail, they release orbs of energy that are absorbed by the Soul Vessels and generate 16 or 18 SOUL.
 * After a certain number of hits, the statue ceases to glow and no longer gives SOUL. It is recharged when the Knight rests at a Bench.
 * There are two standard sizes of Soul Totems, though there are several different appearances for each one:
 * Small (3 hits): 48 to 54 SOUL
 * Large (5 hits): 80 to 90 SOUL

Additionally, there are several unique Soul Totems with unlimited SOUL scattered throughout the Path of Pain. These totems are in the depiction of the Pure Vessel. Many Soul Totems were most likely stolen by the Scholars at Soul Sanctum, as there seems to be an entire pile of them beneath the Soul Master arena.

Soul Caches
Soul Caches are found in the Soul Sanctum in the City of Tears. They are glass jars containing the same orbs of energy as Soul Totems, though they can only be hit once before shattering. Breaking one grants 20, 22, or 24 SOUL. Two more Soul Caches can be found within the Abyss in the lighthouse.

Other Sources

 * Standing in a Hot Spring generates 50 SOUL per second.
 * The Grubsong Charm regenerates 15 SOUL every time the Knight takes damage, or 25 if Grubberfly's Elegy is equipped.
 * The Weaversong Charm combined with Grubsong gives 3 SOUL whenever the Weaverlings hit an enemy.
 * The Kingsoul Charm passively generates 4 SOUL every 2 seconds.
 * Salubra's Blessing generates 50 SOUL per second while the Knight sits at a Bench.

Soul Vessels
Soul Vessels are additional storage for SOUL, represented as small circles to the left of the main SOUL meter. The Knight can acquire 3 total throughout the game by collecting Vessel Fragments. 3 Vessel Fragments are required to make one Soul Vessel. Each Soul Vessel can contain 33 SOUL.

If the Knight gains SOUL while their main SOUL meter is full, the SOUL is instead transferred to one of the Soul Vessels, starting with the lowest one.

Soul Vessels transfer their SOUL into the main vessel when it has empty space and when SOUL is not being used. There is also a small delay between running out of SOUL in the main meter and having it be refilled by the Soul Vessels.

The Nail acquires SOUL for the Soul Vessels at a reduced rate, only providing 6 SOUL per hit.
 * Soul Catcher increases this to 8 SOUL.
 * Soul Eater increases this to 12 SOUL.
 * These effects stack, giving 14 SOUL if both are equipped.

All other sources of SOUL do not fill Soul Vessels at a reduced rate, instead filling them at their normal rate.

It takes more Nail hits to fill Soul Vessels than the Vessels return in SOUL. Because of this, if the Knight is in a long fight and is constantly gaining SOUL to use for Spells or Focus, it is better to use the main meter as soon as possible.

Trivia

 * Team Cherry was inspired by Bloodborne's healing system for Hollow Knight's Soul collection and healing mechanic. In Bloodborne, players can heal if they hit an enemy shortly after being damaged. Team Cherry paralleled this in Hollow Knight, where players can hit enemies and then store the Soul to heal at their own rate.

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