This was a pretty packed chapter.
We met the incredibly cool looking sinners Jenai and Vid. Jenai is shown to be more emotional as he has a deep regret for the death of Rizel and a deep hatred for Joshua for orchestrating that in a way as if without him or his presumable bait Rosette wouldn't have been on her way to fight Rizel in the first place. And in his rage we saw just how scary the often humorous Aion can be as he grabbed the violent Jenai and scared the soul out of him. He went from a raging animal to a scared puppy in seconds.. Chilling. Vid seems to be more business less emotion expressing that it was her fault and Jenai shouldn't blame anyone but her. We can see how the demons are like siblings in Jenai and also that the sinners seem that much closer. I also assume the fact that the non blood demon Joshua has joined the rank of the sinners being named Master drives him mad.
I'm pretty sure Vid mentioned how Fi and Joshua bond due to them both missing something.
I know in the anime Fi is Stella's sister so if that pertains it makes a lot of sense why both would take care of each other. Both are missing and taken away from their very close sibling.
We now know that Fi is a 'limiter' to Joshua maintaining his consciousness. Without her there to do whatever she does he would probably lose everything that makes him him. I'm assuming this is due to the way the horns and demonic properties of it are affecting his body. That's why he wants his sister more than ever and why they're obliging him, because Fi's not enough anymore.
The plane scene showed us a new side of Rosette. She's always in action, and she's always doing something. This was one of the first times we got to see her stuck in her thoughts and it was quite special. It was reminiscent to some of her more serious moments. Rosette gets lost in her thoughts and anxieties about all the things that haunt her. Remington staying back to let her and Chrno deal with it was similar to when he released the monster for her to fight, it's to allow her to deal with what's to come and to avoid doting her so she can deal with it.
Remingtons demon investigations must have to do with Aion's plans.