LF Howler Core Development Materials A material used to break through weapons, ascend Resonators, and upgrade skills.

The Tacet Core of a feeble Howler. It is the remaining part of a Tacetite Bloom after it withers. Despite its astonishing accuracy in mimicry, it only ends one way—reducing to a mass of twisted Frequency Energy.
Sources
Drop: Howlers
Store
Forgery Challenge
Weapon Shop