^ FWIW, my own reading of her character is that she's on the autism spectrum. I have a close relative who has asperger's syndrome and the similarities in the general behavior are quite striking.
I'm admittedly only partway through the game so far so this could be inaccurate since I don't know the full story yet, but it's a spoiler either way even if with incomplete knowledge.
The player character gets straight up Isekai'd to the past so who cares about the descendants, let's screw up the timelines!
I don't think it's ever been specifically confirmed that the characters are direct ancestors of the DPPt cast? Hell, I'm not sure it's been confirmed that this is the actual past and not a pocket dimension Arceus created
yes, my favorite genre, "girls that are rivals for the affection from a stupid male protagonist that doesn't deserve them but then the girls kiss and fall in love with each other"
Adachi actually gets a lot better around her mid-twenties. She can hide her embarrassment better and is generally more cool heaed. Shimamura becomes a happy ditz.