Basically after folks sifted through a zillion codes-within-codes in the game's files, went to secret websites, got codes from there, and so on (National Treasure style), fans figured out that the reason why DDLC is so creepy is that at least two of its characters are imported (isekai'd?) from a horror game called #Libitina.

While the majority of folks who got this far seem to agree that Libitina was supposed to be the horror-on-purpose sequel to DDLC, the game never showed up.

Normally I'm not such a stickler for games *having* to come out, but considering how dense and deep this whole Libitina ARG is, it's kind of a dick move to build up something that big and, when it's found out.. nothing. Not even a "hey you got it, sorry it's delayed until 2030 AD" from Dan Salvato.