This might be the least subtle thing I've ever read and that's okay.
The theme of "talk to your friends instead of self isolating when you have problems" is constantly present and is super well represented. There are very few stories where I think a political activism arc is a sensible plot point, but it fits in perfectly here thanks to the buildup from previous episodes and, again, the central theme.
The trapped in a time loop bit was also very well done. Despite the circumstances it was extremely easy to relate to Rika's situation and to draw parallels with depression, and the talking to and working alongside friends to beat "fate" was incredibly good.
Hinamizawa Syndrome, while a bit out of nowhere, is also a very direct anti-isolation metaphor.
The only reason I don't have this at a perfect score is because I think the plot twist at the end was kinda bad. For a story set in a small town, having the true culprit's main weapon be a private army of goons with no personality coming all the way from Tokyo feels anticlimactic. A complete tonal shift that wasn't foreshadowed particularly well and feels completely removed from everything else in the novel about small town life and interpersonal interactions.