There is actually a hidden story in the game that is believed to become Team Salvato's next upcoming game.
The game's lead developer and writer, Dan Salvato, stated that it was born from his love-hate relationship with anime. In particular, he cited the "cute girls doing cute things" genre to be a double-edged sword.
In the concept art book, Dan Salvato noted that "'Sayori' was some kind of unholy fusion between 'Sayuri' and 'Saori', it's possible that both names couldn't actually pass off as real Japanese names. However, "Sayori" is an actual Japanese girls' name (as well as the name of the Japanese halfbeak fish), albeit an uncommon one.
Due to fanbases "waifu-ing" particular characters, many fans were concerned about Natsuki, as her younger appearance would make certain people seem like lolicons. Dan Salvato himself stated that "all of the characters were 18" (including Natsuki). In Plus, it's outright stated that all of the characters are "over 18".
The game is free because Dan Salvato feared people might feel being ripped off for paying for a game whose plot swerves completely in content and tone after the end of Act 1. Fortunately, the merchandise sales have more than made up for it. The Plus version is sold at a cost, so it is promoted with the horror elements as a selling point.