Japanese has occupied portions of Korea TWICE now in recent history.
If Japan were to ever attempt to invade China again, Korea is the very first place they would take over.
Korea and China share a long relationship that could be friendship but then could also be considered enemies. What's true is China desires to swallow Korea and Japan at one point also harbored such intentions....so yeah.....

Don't worry folks
There's not a single romance or Harem (from the main until side chapter of the novel) only discrimination against China and Japan
Thats about it
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