These are cages to stop grave robbers They are placed over the grave. (ROFLCopter pilot, M, male)

You forgot to mention that it is common that each side has a hole with a different diameter.

The fact that they're running to the left is, I think, related to the Japanese reading direction (from right to left). Also their books are browsed the other way. When the character of a manga comic is running to the left, it runs towards the next image, which is more natural, because it guides the eyes. Which explains it... maybe.