What is Hetaoni ? I looked it in wikipedia but that didn't help me much ...

HetaOni is the Hetalia, fan-made version of a horror game called Ao Oni. The plot is basically that all of the nations enter a mansion that is rumored to be haunted, and they end up trapped in the mansion. There's an, er...creature there that looks somewhat like Tony, which they have to fight. The fans have named this creature "Steve." The nations are stuck in the mansion, and are intent on getting out and surviving.

Later in the story, time loops are introduced, along with a book that refers to magic time travel. Some other characters show up too later on to help get everyone to escape the house alive.

Yeah, I know. Confusing, isn't it? I recommend watching it if you want to learn more, because it's hard to explain.

HetaOni also revolves somewhat around the idea of clocks.

Also, there's a lot of angst and character death. Just a warning I wanna put out there before you start watching it.

It's an RPG game. Read this wiki here:
link