Thanks a lot for your kind words signus! I really appreciate it.
(Spoilers)
Umm as you say it is a bit troublesome if I say "what happens next", and more in this story that the entire point at the end is about "Based on a story that I will make true", putting everything in that hope that you need to use to build your own future. However I can say that the ending is obviously bittersweet and that as you can guess the birthday party doesn't really happen, at least not normally.
Growing distant is not a bad thing though, since sometimes that may be the best to forget about the past and get over the trauma... and Ziva's own obsession. She was also stuck in the past trying to heal Ciar, making it dubious if she was in love, was only a sense of responsibility, or maybe even her own selfish desire to "make things right" and bring that "perfect world" she talks about in Chapter 4 at the arcade.
Maybe even after going past their past they can meet again, and start all over. That would be great don't you think? At the end you can't really know since this is a story full of lies, and whatever truth you try to guess out from it depends of your own interpretation (or at least that was my aim).
Finally about Koishi... you are totally right hahaha. I'm pretty much touhou obsessed so yes, Koishi was a reference for Claire the entire time (and Marisa for Luce to a lesser degree I would say). While writing I would think of her, and then finally when I explained and made documentation for Bonkiru, the artist, she was the main reference I gave him. Never told him to use the same color scheme, only the hair had to be silver for symbolism about the moon and she had to be a loli to make sure it fits with the time Ciar's trauma happened, but since it is a nice color scheme he just decided to use it anyways and go for it.
He did the same for Ausse using Battler from Umineko as the reference (they look a bit alike, right?) and the Baldy using Professor Badass as reference. Although knowing him he could probably work as a teacher too, who knows?!
Anyways thanks again for everything, I appreciate these comments a lot and they help during the hard times of deving (practically everyday tbh). So you all help to make this worth it. Thank you!