Sole Cloud Flying Cave

Cui Heng was transmigrated to another world and the system told him that the new world he was in was a high-grade Xianxia world.
It was a world where Celestial Kings soared the sky and terrifying monsters ruled the lands. The strong would destroy a planet if their mood was bad and Cui Heng trembled in fear when he learned of how scary the new world was.
Thankfully, the system had granted him the protection that last for 300 years. As long as he remained in the safety zone, he would not receive any damage.
With his safety secured, he began his cultivation training for the next 300 years.
Throughout the years as he trained, some people entered his safety zone by mistake.
There was a peasant who was once a monk and a beggar. Despite that, he still had the dream of bringing peace to the land and saving the lives of millions.
There was a noble who was once called the once-in-a-million-year genius. Yet, luck wasn't at his side and his talent fell and was laughed at by others for years.
There was a princess whose only wish was to find her older brother. She could've become a celestial but decided to remain in the human realm to wait for her brother's return.
There was a weak lady who was plagued with illness from birth but had the goal of adventuring and helping the poor and weak.
...
Cui Heng befriended these people and even gave them a few pointers before they left.
300 years later, when the protection period had ended, he had finally mastered the Golden Core. Even then, he was still reluctant to go to the outside world.
But when he did, he realized that the world was merely a world of Wuxia.

Realizing This Is A Wuxia World After Cultivating For 300 Years

After reaching the Ninth True World Realm, one also had to constantly strengthen the laws of the Immortal Domain.

Therefore, a Paramount True Immortal still had to find his counterpart in the other Immortal Lands and refine it into True Nature Essence before using it to increase the nomological power of the Immortal Domain.

Simply put, the cultivation method from the Eighth True World Realm expert was based on killing countless "same bodies".

The Harmony Body was not the projection of these Paramount True Immortal or their scattered souls.

They were all independent people with their own thoughts and lives.

The reason why they became "Harmony Bodies" was only because the laws they cultivated were a little special. They were coincidentally the same or similar to a certain Paramount True Immortal.

Actually, this was not much different from killing people and cultivating.

Immortal Land Harmony, Memory of Hongwu (2)