Ancient fragments, each embodying a primal force:
Thunder - A rare sixth relic, forged not from elemental balance but from raw storm energy.
Crafting high tier weapons with Fire affinity:
Thunderstones are the only elemental essence that can be crafted. Using x4 Air Essence, x4 Power Shards, and x1 Heavy Core.
Elemental Essence can be found in structures as rare loot. Or dropped from High tier Bosses. There is also a small chance to receive a Thunder Stone from defeating Divine Warriors.