Thread:MaximumDepravity/@comment-117.234.178.243-20181231113038/@comment-27272542-20190105060540

It's a rare drop from Mad Water Spirits and Mad Undine.

A couple good spots to farm them are Pure Water Source, Guaracuna Fortress (2 spawns of Mad Water Spirits that can easily be reached) and Great Bank Grebel, Dragon Valley (has a campable Mad Undine spawn, but requires enabling the Katorit flag and forcing Chapter 7A).