It's a fan-made horror game based on the Japanese game, Ao Oni. It instead uses the characters of Hetalia, and it's quite popular among fans.
To summarize, Italy, Germany, Japan and Prussia enter a mansion which is supposedly haunted, and very soon after investigating a noise which turned out to be a broken dish, Japan ends up alone. That's where the problem starts.
More characters show up, and stunning secrets and twists are revealed along the way, all while the nations are trying to get out of the mansion.
Currently, there are 17 parts, yet the 2nd half of part 17 has yet to come out.