"The heavens are fair." this was what many cultivators said about the heavens when they saw how it kept everything in balance with rewards and punishments.
Some said the heavens were merciless and in this this moment, both sayings were applied to Kai Syaoran and the Thunder Emperor.
The two had gotten things that were totally unacceptable in the eyes of the dao and for this, they deserved the greatest of punishments to re-balance the board. This balance could be achieved with their deaths or great injury.