However, the DMS ones have retired and the DBS one... handles bad slash, obviously.

That being said, if the only thing that's egregious about this fic is that the writing is lackluster, I don't really see the point in MSTing or missioning it. Not all badfics are missionable -- what really marks something as mission-worthy is whether or not there's something that would be funny that comes out of it. Otherwise we just come across as nitpicking killjoys. (And believe me, I learnt that the hard way. A badfic whose badness is funny will sustain your interest long enough to mission it, rather than something you just feel obliged to spork because there's a Sue in it.)

That being said, MDZS takes place roughly in the late Tang Dynasty, which did overlap somewhat with the Heian period, so hypothetically it's just a trip to Dongying (the classical name for Japan in Chinese culture, also mentioned in the MDZS novel) for MDZS characters to make it to the world of Onmyoji. So... not as disparate as you may think!