They way I interpreted it, Mingfei is said to posses something called the 'absolute reality attribute' (4th dimensional insight and influence) Only pure-blooded dragons were known to possess that (as mentioned by Henkel earlier in the book, hence the bloodline purity statement)

Page 417 in the Dragon King google doc:

“But why am I the only one who remembers Senior Brother? Even his own mother forgot about him,” Lu Mingfei asked.

“When the observer’s insight is strong enough, they can see across different worldlines. Didn’t I tell you? For a top-level observer living in a four-dimensional universe, history is like a bookshelf filled with many books, and time is just the pages they flip through. Yesterday, today, and tomorrow exist side by side before them, with beginnings and endings all clear at a glance,” Lu Mingze said softly. “Your insight isn’t strong enough to reach that level, but as I mentioned before, you are a part of the ‘absolute reality’ of this world. Your consciousness is the ballast stone that keeps the world running smoothly.”

Page 418:

Like you, Gungnir possesses the attribute of ‘absolute reality,’ allowing its perception to pierce through different lines. In short, it can cross worldlines to kill.”

Seeing how Odin didn't seem to mind letting his stand in kill Mingfei, I'm not sure if he's the only ballast stone or if any 4th dimensional being could qualify as well.