Another question I have for this update is some technicality regarding ghost Sekai.
Why didn't Akira react to Sekai putting words into Ami's mouth right in front of him?
Though it has been revealed that Ami can also sense Sekai's presence, she has plenty of reasons to choose not to call out her ghostly mom puppeteering her due to Ami's own conflicts in interest with Niki. However, Akira would never be able to continue engaging in a conversation normally if he could see Sekai literally acting up and joining in the discussion in front of him.
The only reasonable option for me is that whether Ami could sense Sekai at that scene or not, Akira couldn't see Sekai at that moment. This honestly is quite surprising for me. This not only means Sekai might be able to go cloaking while maintaining her influence (or even choose which individual can see her and which cannot), but this also suggests that she is willing to conceal her presence from Akira, and maybe even Ami, in order to proceed with her scheme.
Both of these are very worrying. I was thinking that at least these two remaining Arakawas will always be able to observe Sekai should she wish to show up in front of viewers and actively participating, but this scene is really telling me otherwise.