(55k words, ~3-4 hour read; read the Baka-Tsuki translation.) Time loop mystery.

Those familiar with novel/light-novel series like Hyouka or The Melancholy of Haruhi Suzumiya (particularly "Endless Eight") will be at home here: yes, there's a Japanese high school classroom, yes there will be a beautiful long-haired girl who interacts with the narrator, yes there will be a silent mousy short-haired girl who looks an awful lot like Rei Ayanami/Yuki Nagato in it who is inexplicably popular with the protagonist & readers, yes there will be a goofball sidekick. But the core of Hakomari is not tired romcom tropes, but rather a somewhat intelligent exploration of time-loops/Groundhog Days: besides the obvious like being able to acquire many skills and 'predict the future', how would you detect the center of such a time-loop and escape? What happens to people over many loops? Perfect time loops are too boring since by definition they cannot change, so what kinds of imperfect time loops are there? Are the 'awake' people really as powerful as they seem, or might the loopers be powerful in some ways themselves, as they can keep doing the same thing indefinitely and can be guaranteed to do so?

The answer to each question may seem to be pretty obvious, but Mikage lets the reader infer an answer and then yanks it away several times, using reasoning that would not be out of place in Death Note or Hyouka, using the out-of-order chapters to, like Memento, maintain suspense and mimick forgetting - mysteries are often as much about figuring out why something happened in the past as what happened in the past. (In this respect, it's a trickier exercise than "Endless Eight", where there's multiple bits of time-travel but they're all straightforward to understand.) By the end, it seems all mysteries have been tidily resolved, and the answers are good.

The riddle aspect works well, but the characters and setting otherwise leave me unmoved. The writing is unremarkable, setting is arbitrary, the characters are (as already indicated) stereotypes, and the ending is both a partial copout in averting a death which had been giving it pathos/depath and also a blatant gimmick for continuing to write the series if the first one sold well enough (which given there's 6 of them now, it must've). The mystery part is fun, but like Primer it's too lacking in the other departments to be more than good.