Nano machine is actually a time travel manhwa and the current timeline we're reading is an altered timeline.
In the original timeline, our main guy Cheon Yeo-Woon is born into a pretty peaceful era. He ends up conquering all of Murim, absorbs several Spirit Beast Cores, basically achieves near-immortality, and becomes this unstoppable Demon G**-level powerhouse. Blade G** was actually one of Yeo-Woon's subordinates, super strong, but he could never beat or surpass the original Cheon Yeo-Woon no matter how hard he tried.
That eats at him so much that he figures out time travel, goes back in time, and starts messing with history. His whole plan is to Prevent Yeo-Woon from ever being born or reaching that g**-like peak. He does this by assassinating key ancestors in the Cheon family line or crippling the Demonic Cult's power so it never dominates.
