Sarugatsuji

Under the influence of the Chinese cosmology imported by the Imperial Court in ancient times, the northeast direction (艮) became an object of superstition.

'demon gate'), was believed to provide a means by which evil spirits and bad luck could enter.

In order to prevent such things from entering the palace grounds, the northeast corner was built in an unusual concave shape.

By avoiding a convex vertex pointing in the direction of the kimon, the wall, and indeed the entire palace, could be regarded as technically having no "northeast corner".

Tanaka Shinbei's sword was found at the scene of the murder, but he denied killing Anegakōji and performed harakiri during his interrogation.