The Hetaoni characters are based on the Hetalia characters. The gameplay of Hetaoni is based on Ao Oni.
No, the "trailers" on Youtube are just fanmade videos for Hetaoni. Hetaoni is an RPG game that is based on the Japanese RPG game Ao Oni, but its characters were changed to those that appeared in the manga/animate Hetalia.
This is a relatively subjective question, but many Hetalia fans and Ao Oni fans consider Hetaoni to be a fun game.
A few 1st tier games based on Ao Oni are Abe Oni, Aka Oni,Akame Oni, and Ao Oni Plus.
Yes, there is one novel that is based on the Ao Oni game.
There are 5 official novels based on the Ao Oni game series.
The main protagonist of Ao Oni is named the same as Ao Oni.
One place that Oni appears in Ao Oni is in the library.
It is thought that the Oni is inside the mansion because he was a former resident of Ao Oni.
The Oni in Ao Oni is a creature with light purple skin and large black eyes.
When an Oni starts following you in the game Ao Oni, the only place to hide is in a closet.
There are not solutions on the Ao Oni. This is a puzzle game that is made in Japan.