Nio Guardians or Benevolent Kings keep guard at entrances to Buddhist temples in Japan and their job is to ward off evil spirits.
They were brought to Japan from Idnia some time between 7th and 8th century and always stand on two sides of the first temple gate, called Nimon (literally Nio Gate 仁王門).
The guardian on the right has his mouth open, the one on the left is thight-lipped.
Each is named after a cosmic sound.
The open-mouthed is called Agyo, since he is uttering the sound “ah,” meaning birth.
The close-mouth goes by Ungyo, which sounds “un” or “om,” meaning death.
Thus, the two together represent Alpha and Omega, beginning and end, birth and death.
At Shintō shrines, the Niō guardians are replaced with a pair of koma-inu (shishi lion-dogs) or with two foxes.