The Four Guardian Kings are mighty protectors of the Buddhist law. Clad in armor, they stand at the four corners of a Buddhist altar, protecting the principal image. Each represents one of the four cardinal directions. The aggressive stance and grimacing demeanor are standard for these guardians, whose mission is to ward off evil.
The Four Guardian Kings, in similar style, are illustrated in Miho Museum, ed., Omi: Spiritual Home of Kami and Hotoke, exh. cat (Shiga: Miho Museum, 2011), pp. 220-21.