There were two main ways to kill an Undying with an undying body: soul destruction and forced annihilation.
One was for an expert at Peak Marquis or above who specialized in souls to kill them through soul destruction.
The other was forced annihilation, using an absolute advantage in power to destroy the opponent's immortal divine power and wipe them out completely.
Once all their immortal divine power was annihilated, the opponent would naturally die.
There were two kinds of forced annihilation.
In the first, the gap between the two sides was enormous.
A Peak King or Limit King could kill a Marquis Immortal with a flip of the hand, without paying any price at all.
When the difference in level was too great, destroying an undying body was easy.
In the second, the gap was not quite so large.
If an Initial King wanted to kill a High-level Marquis, they could shatter their opponent's divine body again and again, but the opponent could keep reforming it without suffering any loss.
In that case, killing the opponent required paying a certain price.
That meant burning their own immortal divine power. Once burned, that portion of immortal divine power was permanently lost, along with the fragment of soul contained within it.
This was a permanent loss.
Thus, even an Initial King could do nothing against a High-level Marquis if they wanted to avoid burning their divine body and paying any price.
But once an Initial King burned their immortal divine power, the attack power unleashed in that instant would be terrifying, rivaling a Peak King's. Naturally, they could then forcibly annihilate a Marquis.
Even an Initial King would need a hundred or a thousand years to slowly recover after forcibly annihilating a High-level Marquis, unless they used expensive, precious materials specifically meant