Overview[]
This is what the Dark Thunder Essence looks like.
Dark Thunder Essence is a demon part that is dropped by Kaigaku after defeating him along with his collar. Kaigaku can drop 1 Dark Thunder Essence. The only use of this is for crafting the Dark Thunder Katana if you are a Thunder Breathing Hybrid. It is still unknown if this item is going to get more uses In the future.
Unfortunately, similar to the Blue & Green Horn, and Crystal Essence, you cannot sell this to John despite being a demon part. However, you can trade this to different players(more specifically, a Thunder Breathing Hybrid player.) who wishes to get ahold of Dark Thunder Essence if you don't want the item in your inventory.
Talk to Kaigaku at the forest hideout for the dark thunder sword.
Can be sold for 2-5k (Depends)