Well I went through all three parts of the story, so I'll put my thoughts here- I think the story's pretty interesting so far, the characters are interesting and relatable. Rika's a good lead with how her internal dilemnas and issues keep mirroring the things around her, and the over-arching mystery is unique but still, uh, mysterious. Guess I'm waiting for more in the future.
As to the mechanical aspects, I think overall the writing's very good and flows well, the dialogue is snappy. Only thing is how San uses full stops/periods for all her sentences- I understand the internal logic of making her blunt and as if all her words are statements, but I think it kinda reads awkwardly and can make it a bit muddled. Also, I think it'd help if you added a visual effect filter over the backgrounds you use to help unify the feel of the VN a bit more, they feel a bit mismatched and it'd let you obscure some of the more visible details in an artsy way. YMMV, of course
apart from that it was really good! I'm looking forward to the next installment!