The War Ash, when applied to a weapon, imbues it with the Heavy attribute and imparts the following technique:

"Earthshaker's Resonance: Execute a forceful double-handed slam upon the ground, causing a seismic upheaval and unleashing a powerful shockwave. Perform an additional input for a secondary ground-shaking impact."

Applicable to all close-quarters weaponry.

These ashes are discovered within the Elden's Throne situated in the Gray City.

Upon overcoming the formidable "Initial King" Ge Fulei as the final adversary at this location, you acquire the memory of Holly Lu.

To obtain the War Ash, you can utilize the Reminiscence feature at Enya, the benevolent guardian, in exchange for these potent remnants of conflict.