If ANN’s episode titles are correct, it looks like…
(no fancy spoiler tags here, so below the fold it all goes)
...Rubi's story is squeezed down to a two or three-parter, with the remaining episodes focused on the enforcers.
In the manga, Rubi’s story takes a full five chapters, but that doesn’t make sense here. The end credits have the enforcers from chapters 8-11, and even if they’re collapsed down to a two-parter, the only things left to use would be 6, 7, and 39. Chapters 20-28 are pretty much one story arc, as are 29-34, and the school festival in 35-38 requires chapter 6 to make sense. Chapter 40 is more of a new-season intro, since it was written as a standalone introduction to go with the change in magazines.
So, the choices are:
I don’t realistically see them animating chapter 6, because someone would have noticed her in the credits, and if they aren’t doing the school festival, she’s just another monster-of-the-week. If they get a second season and decide to use her, her intro can be dropped in pretty much anywhere.
You could make a pretty decent second season with chapters 6 and 29-40. You could make a dark second season with 6 and 20-34. I’m not sure you could get something coherent if you tried to include significant elements from both 20-28 and 35-39.