I'm bound to the World-Destroying Witch

After Xia Feng transmigrated, his heart was inexplicably ripped out.
Instead, there is a damaged Demon Heart, whose activity is only enough to last for eighteen years. This is a magical heart that can synchronize the strength of the target.
In order to survive, he bound himself to the future world-destroying villain, the world-destroying witch.
The stronger the world-destroying witch is, the stronger he becomes!
Then Xia Feng realized, "It's no wonder I stirred up trouble: Miss Witch, I admit you're strong, but not strong enough!"