
Roland is getting the labor force he desperately needs to ramp up production and eventually start his own industrial revolution. But black spots?! How scary~ Does it remind you of anything in our world's history?

In our world's history yes. Correct! Now that the plague arc has finished, I can say that while similar to our black death, it is not in which the bacteria have been modified. The biggest spoiler that kept me from talking about it is that the bacteria had been magically + scientifically modified. You can infer this by Roland and Nightingale's reaction as well as the revelation of the church keeping
"useful" witches instead of just turning them all into fuel for their powerful zombie army.

I don't like how the translation team didn't explain what a furnace is but honestly... Translation teams tend not to explain a lot of things when it comes to wuxia manhwa so whatever lol.
From what I learned in another wuxia novel, a furnace is a woman who strengthens a man's cultivation with her body. In the novel I read (not sure if this applies to all wuxia), the woman remains weak and cannot cultivate herself due to the fact that she is a furnace. She can only use her body and energy to strengthen a man's cultivation thru sex rather than use it to strengthen herself. This makes them extremely valuable lovers and, more often than not sadly, rape victims.
I'm not sure if in Magic Emperor the exact same thing applies. Ning'er might not be born as a furnace but chosen or she might just be weak on her own (or just in comparison with the other two) and not because she can't cultivate. Regardless tho, by the MC stating that none of the brides come back and implying that they all die, he was also implying that, as a furnace, she'd be raped until she died if she went ahead with the marriage.

I bet she's Howen's wife

Eh true, I honestly forgot about that. It also wouldn't explain why he went to a ball with another man's wife so I guess my wife theory is out.... Well then again he could have been dreading going alone so she went with him. He is desperately trying to stay married after all, despite seemingly not being in love with the MC or even having met her before.
I really felt for Heidi when she started blushing in the background from that hot display of power and Melissa simply calling her name afterwards.