Overall I found the story quite interersting surrounding the tennyo and the mountain beasts. You have parts of the main explanation in Ginko's route with what the mountain beasts actually are and how they were transformed into one and in Shouko's route + the Sinsemia route the explanation of the cursed stones that Shouko is able to see. I found the "True route" a bit strange because - maybe only due to my limited compehension skill - they based it on Sakuya's ending, but also used parts of Shouko's route in it (which might just be more unusual). The whole Shouko and Sakuya being posessed wasn't really to my liking somehow. I know from the fragments that Ginko's sister cursed her core fragment of the heavenly garb and merged it with the lake before stabbing herself with a katana and that she wished to see her lover again, but I feel to have missed the connection for why her "essence" remained in the red "command stone" or if every of the red stone contained her "spirit". The final showdown was quite good despite being a bit corny with the use-the-past-to-break-her-free method
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On to the individual routes/characters:
Ginko: As I said in my earlier post, her route was quite funny in terms of how she has a teasing character trait, but is totally clueless about sex-education. We get to know she's the younger sister of the celestial nymph who we see in the fragments (I hope I understood that correctly). And that Kousuke's mother saved her at one point in time. But outcome of her route pre-epilogue was sooo anticlimatic. We have Kousuke and Co. depressed because she hasn't showed up since her battle with Mizuchi and all of sudden and as if nothing happened Kousuke meets her at an ice-stand and they talks "too" casually. I was a bit confused in the true end because I thought it was mentioned that she had to return to the sky to heal her wounds for a long time, but then we meet her at the festival and she said she couldn't return afterall or something like that. Seeing her going all-out and heavily damaged was well-done.
Iroha: The confession moment was quite boring, but the whole conclusion of her parents being the monster who saved Kousuke was moving with Kousuke taking the burden of killing it on its request and when the monster wants to meet Kousuke alone with Ginko as interpreter. Her character was okay, though the first impression when Kousuke spied on her dance practice was very misleading
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Shouko: I found her character development the best. You can clearly see how she regained her cheerful personality the more time she spent with her Onii-chan. Though as a blog mentioned there's no way she's of full age and the lead up to her ero scene was bad. Her changed appearance in the true route was veeeery cute and "NGHHHHH". Her appearance of the "bad ending" in her route was a surprise, though. Maybe the part I didn't like that much was her innate "dislike" of Sakuya on Sakuya's route even though I could understand the reason for it. I didn't think it was explained why she was able to see those cursed stones other than the stealth-mode Ginko mentioned in the true route or if her strange dream is connected to it.
Sakuya: I loved her route as it had very tender moments between Kousuke and her like when he hugged her when she wore her mother's clothes or the first kiss build-up in present timeline. It was very well done in contrast to the more drama-loaded moments in other VNs with incest option (à la Natsu no Ame or KoiKishi). The conclusion if you decided to tell Satsuki the truth was done very, very swiftly. What I wished for in her route was more focus on the past incident where their mother saved their life. Sure it was explained in Ginko's route and the true route when Ginko released the "seal" of his memory, but on Sakuya's route you get directed a few times in this direction without any real resolution and I felt that her character development wasn't much outside the romance. Still, the tender moments made up for it.
True route: After playing Whirlpool's Suzukaze no Melt and Lunaris Filia where the name of the true route is connected with the character focus in it, I was left dumbfounded that the "Sinsemia route" was nothing like that. I cannot remember that the name was ever mentioned during it and I thought at some point a character with the name would appear. Ignoring that, I liked how the makers decided to base it on Sakuya's ending and made her the "canon" girl.
Points I didn't completely understand: Apparently there were many red stones, but did each one contain the "reduce-human-quantity" persona of the Nee-san Tennyo? We see Sakuya being affected by it after she licked the stone in the flashback of their childhood and Shouko on her route. But then the "evil spirit" of Shouko jumped suddenly to Sakuya.
And all the mindscrew just because the Tennyo must have gone mad and wondered in the last fragment when it was and decided that the world should become hell and puts a curse on her sister's decendants. Pretty harsh X_X