The Northern Domain Three Evils have been able to dominate the Dan State North Territory for many years not only because of their formidable strength but also because they have no families, no turf.
They are solitary and unattached, with no concerns.
Whoever wants to deal with them must think carefully about the consequences.
If they can be killed on the spot, then naturally there is no problem. But if they cannot be killed, then there will be big trouble.
The Northern Domain Three Evils are the type who seek revenge for the smallest grievance. When they seek vengeance, even a Great Sect like the Ten Thousand Sword Sect would have a headache.
Today they kill a few of your disciples, tomorrow they set up an ambush for one of your Elders.
Who wouldn't fear them? Who wouldn't have a headache?
Upon reaching the Sword Saint Realm, one can control their sword to fly and come and go like the wind. To kill all three evildoers in one go is very difficult.