This is an extremely crazy idea. Even for Integration Cultivators, let alone Tribulation Crossing Realm cultivators, very few can accomplish this.
Because wanting to cleanse the Demon Occupied Zone in a short time comes with two major challenges that need to be overcome.
First: Siege warfare is by no means an easy task.
Defending a city is easier than attacking one; the Demon Race defending a city, taking advantage of the terrain, will surely not be an easy bone to gnaw.
Not to mention one person, even a fully equipped team of cultivators would find it as difficult as reaching for the sky to capture a demon city in a short time.
Additionally, if we cannot break the city quickly, the demonic cultivators from other cities in the Demon Occupied Zone will come to reinforce, making it difficult to even retreat, let alone break the city.
But Lu Qingshan is different.
Because he is a lone Sword Cultivator.
