I think you underestimate just how SHORT certain chapters of the series and how much content you can fit into just 12 episodes of anime, unrelated manga but I'm going to use it to prove my point "chained soldier" is a pretty action packed manga just like this one with similar chapter lengths maybe longer, the first episode consisted of ENTIRELY the first chapter of the manga which was 60+ pages, yet STILL ended season 1 at about chapter 42-43.
So I think you might be pleasantly surprized with how much content they'll probably fit into this anime, me personally I'm predicting stella to show up, about episode 5 or 6?