If North Korea is not a threat then surely China wouldn't be either. Admittedly the Chinese seem to hold a grudge for a very long time over the Nanking Massacre, but I cannot imagine them attacking Japan.
Fable and history are merely tools of statecraft. The decision to go to war or not with anyone has much more to do with resources and trade routes than anything sentimental. As long as China is getting its way, and Japan does not become weak, Japan is safe. But at a certain point China will outgrow its current situation and will find it necessary to make territorial gains in order to keep growing, or something will get in its way, like the US. When that happens both sides will come up with a narrative that gives it them an apparent moral highground, and we get a war.
Wha seems to be becoming difficult now is reading the enemy's movements, because there is so much activity it is easier to hide significant events in plain sight, like the building of underground installations, etc. Unknown unknowns are the scariest thing of all.