The void heart charm is a charm that takes multiple steps to put together. This charm will allow the player to unlock two endings as well as access the Pantheons. This is no easy task, but you will be able to get it done.
Requirements
How to find the Void Heart Charm?
- Gather 1800 Essene
Essence can be found from defeating dream bosses (1,600 total essence) and dream bosses (1,100 total essence).

- Upgrade the Dream nail to the Awoken Dream Nail
With 1,800 essence go talk to the Seer in the resting grounds. You will need to talk to the seer over and over to get all of the rewards.

- Get into the White Palace
From the Hidden Station head to the left and use the newly acquired awoken dream nail on the Kingsmould laying on the ground in front of the White Palace.

- Get through the platforming
This will take you to the dream realm where you can follow the difficult platforming path until you reach the Pale King and ultimately the 1st half of the king’s soul charm

- Collect the other King’s Soul Fragment from the White Lady in Queen’s Gardens

There is a shade gate blocking the way as well as a boss fight with the Traitor Lord

- Both pieced put together creates the Kingsoul Charm

- Equip the King’s Soul Charm and take it down into the bottom of the Abyss
This will open a new path at the bottom of the Abyss

- Collect the void heart
Follow the path down and to the right. Eventually you will come to a black egg with the little knight’s reflection. Dream nail the reflection to acquire the Void Heart Charm.

With the void heart charm you will then unlock two endings when fighting the Hollow Knight in the Black Egg temple. I will leave that to you to discover.