Yoru/Asa are going to turn Denji into a weapon in order to kill the Death Demon. Yeah that's my prediction for the ending.
What even is good art? That's entirely subjective. If you ask me, the backgrounds are always detailed with characters having very simple designs but what Fujimoto excels at is paneling. It's always easy to read and that's what's good about it in my opinion.
There's always open spots for official mistresses or concubines
The backgrounds I'm guessing are done by assistants. Which is fine imho, plus Fujimoto isn't exactly hiding it what with the huge difference in style between backgrounds and characters, like you said.
Not likely, first, she's like sister for him, and some controlled person wouldn't do for Denji, on other hand, in the end of 1st part he also saw how Makima wanted Chainsawman, and Denji was just a dirt that surrounded CM heart for her, so I'd think he's intrested in gaining somebody who likes him and not chainsawman (except he still confuses people liking CM with people liking him, which I find a bit of retcon of his progress).
