I am adoring the whole conflict that Lavi having with himself in terms of acting as a 'Bookman' and as a friend. Especially the last two chapters of this volume. The look he gave Leverrier gave me chills.
It's also fun to note how close Kanda and Lenalee are without them interacting that much. Kanda calling Lenalee strong is just proof that he has high regards for her, which is rare for him.
The concept of an akuma evolving more and more to look like a human being is also interesting, which Bookman touches upon. This is the first Level 4 the Order has ever encountered, and with each 'level' we see more human characteristics evolve alongside the akuma. From mindless weapons, to weapons with thoughts/language to a level three that looks like a skeleton of a human being, we have seen this process happening already but it is even more dramatic with the level 4. The fact that it has both male and female characteristics (looking at the chest, we can see this) and is almost "child-like" represents duality and deception. The more powerful the akuma becomes, the more it resembles a human being. A child's mask can throw us off with the promise of 'innocence' (oh, the irony).
What I'm looking forward to learning is why the level 4 reacted to Allen crying the way that it did and whether or not the Earl has any control over this type of akuma. Seeing as it blasted the skulls, it seems impartial to whom it kills. I'm going to stop ranting now, there's just so much to think about.