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

In the Endless Chaos Sea, Cui Heng clapped his hands gently and felt the subtle changes in the past timeline. He could not help but sigh in his heart. "After reaching the Peak of the Mid-stage Return to Void Realm, there's no need to make any changes to the past. It's more hidden and difficult to detect."

As he directly attacked using "his past self" and did not cross the River of Time to attack the past, the River of Time did not show any clear fluctuations.

Even a perfected Heavenless Realm Immortal Emperor would not be able to discover such a change in the timeline.

This was because no matter how powerful an Immortal Emperor was, they were still entangled in the River of Time. After enduring a huge amount of the corrosion of time, it was impossible to differentiate such subtle time fluctuations.

Only cultivators who had reached the Mid-stage Return to Void realm could easily sense the abnormality of the past.

Going Back in Time, Space-Time Dao Mark (2)