This is a really interesting story and setting, but... I dunno, most of it didn't quite click for me. The art is really neat, of course, and the whole game's composed in a way that gives it a good atmosphere. It just feels kinda incomplete in a lot of ways. I'd definitely like to see an update to this.
It keeps introducing a bunch of crazy concepts and then not really following up on them. A very interesting AU (?) setting gets talked about in super vague terms, the nature of that note Renko got doesn't seem to be elaborated on at all, and the protagonists' motivations feel kinda muddy-- as in, they start out following a weird timey-wimey note because why not, but in the second half they seem more concerned about Merry taking a trip to the future so she can date Renko than whatever the creator of that note had in mind for them to do.
By that same token, I generally didn't think the very chill writing fit the plot. The story seems insanely high-stakes (the way Renko talks about how screwing with time has affected the world makes it sound like she and Merry could cause the end of the whole world/universe as we know it with just one mistake) but it never really feels that way-- they spend most of the game talking really casually, and glibly handwave away the super scary consequences of their actions as "wow we're really playing with fire, huh?". Also, there's a few writing quirks that I found more funny/charming than anything, but really detract from the tone the game seems to be going for-- the biggest example to me being when Renko makes a joke and "(joking)" is added after the end of the sentence.
Few more nitpicks-- most of the choices seemed really similar, to the point of a lot of them feeling unnecessary. Also Renko being depicted with a standard VN sprite was slightly confusing at first, since she's on a screen the whole game, but it wasn't an issue for me-- I just think it'd be a nice touch if, say, the background was split between time periods on left and right sides of the screen, similarly to the Day 10 CG but for most of the game. And I do kinda wish the text moved quicker-- I almost went through the game a second time to get other endings and clarify some things, but the text speed being so slow kinda killed it for me, and pressing Z to skip didn't work because I played on browser and the game didn't save my data after reloading the page.
In short, it's like watching a really cool sci-fi show with a busted TV-- it feels like I'm missing a lot of really interesting high-concept storystuff under the static, and that's a shame.
Also, apologies if I sounded harsh in this comment. The game's neat, and to be honest I feel like I didn't quite "get" large parts of it. If there's some important stuff I missed and my big criticisms here are only because I can't read properly, let me know. And either way, I'd definitely like to see an update to this-- it's cool.