There's something really going on that's a missing puzzle piece here. It looks like Shi-chan isn't that bratty as we've think she was in the past, well for her childhood past at least and was pretty close and gentle with A-chan.
There's definitely a setup on regaining her memories fully here and we'll see what was the actual Shio of the past like. We're only given fragments so far (a bitch, bratty, headstrong etc...) from the perspective of others but there's likely more to that and a reason why she started acting like it that only she knows. We haven't seen her past self's backstory yet and reasons for her actions and it's likely her regaining her memories will reveal this. We've seen Shiori's perspective of her current self, but we don't have any clue on past Shiori's perspective.
I also get the feeling that the relationships aren't set in stone yet, there's a chance for Akio x Shiori here as it might have been the case in with past Shiori. I feel like past Shiori was a brocon lol but haven't had the guts to tell A-chan, add the fact that she did know in the past that they weren't related which would justify that love on her mind.
Thanks for the chapter!