Question 1

Where is Happy yellow post box?

Accepted Answer

Happy yellow post box is in Kashihara, Nara, Japan. You can see its exact position from the map coordinates and the Street View link.

Question 2

Which scene of Beyond the Boundary does Happy yellow post box appear in?

Accepted Answer

Happy yellow post box appears in EP2 of Beyond the Boundary.

Question 3

Can I visit Happy yellow post box?

Accepted Answer

Yes. Happy yellow post box is a real place you can visit. Check what it looks like on Street View before you go.

Question 4

Where was Beyond the Boundary filmed?

Accepted Answer

Anime and manga are not filmed the way live action is. Their backgrounds are painted from photographs of real locations, and Happy yellow post box is one of those real places (EP2).