It’s fine. The characters’ nonchalant attitude to something so clearly abnormal is good bit. Adachi doesn’t investigate any further because her sole interest in life is Shimamura, while Shimamura is so disassociative all the time that she just rolls with it.

If you want plot relevant alien gremlins, I’d recommend Yuri Yuri Panic or Project Yuriforming! Stardust Telepath is another yuri with an alien theme, but I don’t know if it’s ever confirmed that the character is an alien.