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.
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.
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.
Jillian Ashcraft, Monika's voice actress and the singer of "Your Reality", "prefers staying private" for now. There are a few videos online of her singing (she also plays guitar), but not much else.
According to a tweet by Dan Salvato, he originally wanted to release the game on April Fools' Day as the game was already a subversion of a dating sim. However, he felt like the game wasn't fully ready at that point.