Played through the update a while ago. Just wanted to give some thoughts on our proper introduction to Sekai...
Sekai, having broken whatever barrier (Sensei's mind?) was holding her from existing, is back.
The fact that she worked alongside the angels in the events leading up to Makoto and Futaba seems to imply her being connected to the god Yasu worships, and as someone else had mentioned a few pages back, perhaps Sekai may very well even be this god.
Going off that, at the very beginning of this update Yasu makes it clear that her god is on the beach. Later when weirding out Sana, Yasu mentions the fragrance of an Angel, or rather the "scent that comes from the thoughts she (the Angel) thinks and the things that she will see behind closed doors" considering these 'doors' that are opened by the narrator at the end of this update end with the narrator cutting it short prior to Sekai talking does play into the idea of her being the narrator.
Speaking of our final door that we see opened involving Yasu implies, at least to me, that we may be seeing Yasu acting rather different come next update. Something mentioned in the same scene talking about the Angel's fragrance, Yasu mentions how "All of my actions are predetermined by god and the only one who can puppet this fragile body is Him".
Going off the idea that Sekai is no longer 'locked away' and going under the belief that she is Yasy's god, Sekai may plan on a much more permanent puppeteering of Yasu as a means of interacting with Sensei or anyone else (Ami, for instance.). In another direction, even if Sekai isn't Yasu's god, I got a feeling that Sekai's interest in Yasu at the end still involves using her as a vessel. This based both on how sensitive Yasu is to these outer forces and as she puts it when talking to Sana "Indulge. You are free unlike me. You can let them in" which I take as meaning that Yasu can't exactly prevent gods/angels from 'entering' her.
This thought of what's happened to Yasu has been burning a hole in my head for a while now, figured I'd share it. Same time, I could be off the mark here. Hell, on a slightly unrelated note, maybe the reason Sensei now has been given this apartment is so he can avoid Sekai if she has actually willed herself into being alive within the world.
Either way this update was wild, I'm very interested to see what will occur come next update.