Hey! Yeah that seems to be a glitch, it's fixed in the backer version that will release next month. That being said, the best I can say is to go back to before you fought the slime boss and try again.
There's 2 main routes that have like 14-15 variations each. It is possible to save everyone in 1 route yep. In another route 1 person is guaranteed to get a bad end.
Hey! I'll be fixing that in the next backers release, the possession logic kind of was dumb on my part. Anyways, if you can get her to possess you enough it'll solve itself in about 4-5 weeks or so.
Hey! Unfortunately I am having problems with the artist who was commissioned for the slime sounding scene which is why it has remained undone for so long. Hopefully I'm able to get it done soon.