Killing a Harmonization Realm expert is incredibly difficult. The number of Cultivators who have reached the Harmonization Realm over the years is small enough to be counted on one hand, let alone the number of those who have fallen.
All who reach the Harmonization Realm are prodigies who shake entire regions. Their long journey to this point inevitably ties them to numerous factions, they build their own power bases, and their personal strength is immense. Therefore, they rarely fall under normal circumstances. Even between two sworn enemies, a battle to the death is not a light affair.
Those who cultivate to the Harmonization Realm inevitably cherish their lives. Of course, this caution doesn't extend to ants; they can simply crush them underfoot.
In other words, while Harmonization Realm experts may appear domineering and arrogant, as if they hold nothing in regard, they actually value their lives immensely.
