I knew that some additional complications would have to come up to keep the story arc rolling for a full six episodes, so it wasn't much of a surprise to see that a threat to the train as a whole on the agenda. Given the way this series has gone so far, it also wasn't much of a surprise to see this diversion going deep into the Nasuverse. The Child/Forest of Einnashe and the 27 Dead Apostles are two things that I don't believe have come up before in animated TYPE-MOON content but they are integrally involved in more expansive TYPE-MOON lore. As I understand it, the reference to it specifically being a “Child” means that it is an offshoot of the actual Forest of Einnashe and not the actual Dead Apostle by that name, which explains why Callebaut (the priest guy) refers to it as being controlled by an Apostle. The bigger question at hand here is whether this is a part of the overall scheme concerning the stolen relic or an unrelated threat, though the timing and placement seems too suspicious to just be the latter. Besides, something definitely did specifically divert the train towards it.
And there's even more going on beyond the Forest. Hesphastion pops up again and seems much happier about fighting Gray than going after Waver. We'll see next week how well Gray fares with that after applying her first power-up. Olga's discovery of the dimensional pocket, and the ensuing revelation of Trisha's head having been tucked away in it, raises a whole further boatload of questions. As to why it was put in the pocket dimension, I'm guessing that it was done so that the Mystic eyes Trisha had couldn't be tracked. The revelation that the pocket dimension's aperture only triggered for Olga because of a family connection suggests that the killer is from a branch family, and the investigation of Kairi and Luvia off the train suggests that the killer has a previous reputation. I am inclined to believe that Hishiri's presence is a red herring on who the culprit is; I suspect that next episode will reveal that she was just looking for Trisha's Mystic Eyes herself. This is also the second time that Trisha's amulet has been focused on, so that has to mean something that's probably directly related to the killing.
Finally, I can't forget to bring up the zombie cooking show. I know zombies are popular these days and cooking shows have always been a thing, but combining the two is just absurd. The series has not been above being silly in small doses, and this is a great example. Jean-Mario Supinerra seems to be a series-original character, and that Trisha had also approached him about the previous killings similar to her own is another interesting piece. I am eager to see how all of this will eventually come together.