The first couple of episodes builds towards something like that. Then the story gradually loses balance and becomes about a one-sided, obsessive and unrequited puppy-dog infatuation of one girl for another who doesn't seem to care much about anything but herself.
Sounds familiar? That's because it is. It's basically the same premise of that other horrendous and disturbing Yuri/shoujo ai anime, Citrus, though the characters in Adachi to Shimamura are somewhat less obnoxious and sociopathic.
I don't know why love between girls is so hard to write for light novel authors and mangakas, but they always seem end up this way. The relationships are portrayed as essentially unnatural - as something that inevitably results in toxic, unequal and deeply unhealthy dynamics with possessive behavior, borderline stalker obsession, emotional abuse and general creepiness.
Other notable examples of these toxic relationships in shoujo ai are Bloom into You and Fragtime.
In all the above mentioned animes, relationships between girls are depicted as unequal - with one girl who has an unhealthy and cringy obsession with another girl, who is generally emotionally distant and cold and doesn't necessarily change for the better by the end. There's also copious amounts of emotional and/or physical abuse in several of them.
Adachi to Shimamura leaves you with a bad taste in the mouth. In the last inner monologue by Shimamura - the object of Adachi's creepy obsession - we learn that Shimamura is basically just using Adachi's infatuation to not feel lonely and that she'll go along with it until some day she'll be on her own again.
How... ROMANTIC!
This isn't a love story. It's a story about a lonely girl who becomes obsessed with another girl who suffers from chronic boredom and goes along with it for a bit of entertainment. It's sad and depressing and creepy.
Oh and there's a space alien girl too for whatever reason. I assume there's some point to that in the manga this was based on, but in the TV show it's just utterly pointless.
We deserve better shoujo ai than Adachi to Shimamura, Citrus, Bloom into You and Fragtime. But I guess this is all we can expect from a society as conservative and patriarchal as the Japanese. I've yet to see a satisfying and realistic story about love between girls. But if you have to pick one among the ones I mentioned, Bloom into You is probably the least terrible.
