The Amaranthine Prism is an item dropped by Mamon Souldrinker that reduces your willpower but increases your ego, it starts off with -1 Willpower and +1 Ego; once you equip it, each will increase with the passing of time, so it can take your willpower into the negative (modifier) while boosting your Ego through the roof. Each increases every five-thousand turns, although traveling overland consumes much more time and will make them increase faster.
This item is cursed; you can not un-equip it once it has been equipped. Additionally, equipping it makes it impossible to complete the quest Raising Indrix.
Be warned that when your willpower reaches 0, you will die. Equipping it is therefore a death sentence in the long term.