Inside the cocoon, more and more cracks appeared on Karsha's body as the Demon Fruit essence continued to transform the very fabric of his being.
The main reason Karsha consumed the Demon Fruit last was due to the system warning him of the possible side effects.
While there are various easier ways to awaken the Darkness element, using the Demon Fruit is considered an unconventional method. In fact, if an expert found out Karsha had used a Demon Fruit merely to awaken his element, they would either cough up blood in outrage or kill him outright for wasting such a valuable treasure.
The Demon Fruit is meant to be used when comprehending Darkness-related laws like Death, Decay, and similar concepts. Using it as a mere trigger to awaken an element is something many would consider a waste.
However, who is Karsha? He is someone with a God-killer system destined to battle and kill gods. Using a Demon Fruit to awaken an element is but a normal thing to him.
