Out of every loose thread, the one I am perhaps most worried about here is Eiji , because at any given moment in time he could just accidentally condemn them by forgetting that he was not supposed to talk about his "daytrip with Marie".
Like, everybody else involved in this definitely has their own things they want to hide, like the assistant manager or mystery bad vibes dude from the end of the chapter, but Eiji is sitting on a really dangerous secret, and has no idea or reason to assume that it is one.
...also the way they disposed of the body seemed less than safe to me - there's a good chance that suitcase will be buoyant, and end up being washed up on some beach. Which is nothing that Akira would have spent much time on thinking about with her previous murders (after all, she doesn't really do the whole planning ahead thing), and honestly, I could imagine that somebody even found some of the previous bodies she disposed of. After all, for those murders she was hired, she likely had no personal relation to the victims, so it would be harder for the police to track her down even if she left evidence behind.
With the manager, that is not the case anymore.
So, uhm, yeah, really wishing these two the best of luck, they will need it!