That was a bit of a shark jump there
Huh
My current thought on what is happening here from a meta-narrative point is that to the author, Kaede has essentially learned all the lessons he needed to from his traumatic experience. His "character arc" as it were is near complete, and the last step he has to take is to "fight his demons / face his fears" to show that he is now a stronger person. The author decided that his "demon" to fight is the actual instigator of his trauma--Sensei from his past, back and with a vengeance.
You can kinda see this to be the case because when Sensei, Kaede, and Tsubasa start talking, they don't talk like, actual people, but like philosophies or ideologies clashing against each other.
Now, do I personally think this was a good narrative decision to make?
Well ... not really?
Disregarding how whiplash-y this all is, it's not very realistic at all to me I don't think.
There are real people with trauma from experiences of abuse or harm, and they don't usually get the luxury of confrontation their abusers and then that's that and they can move on. You unfortunately will be burdened with that baggage for a long, long time.
Now I thought this mangaka knew that, because this felt like a pretty realistic portrayal of abuse and trauma, at least up to this point.
Just couldn't land that ending I suppose.
I hold my tongue and see what the final chapter for Kaede holds