Shijokobuccho, prajvalosniisa in Sanskrit, is a kind of Buddha that is a deified protuberance on the top of the skull of a Nyorai (tathagata), i.e., a form of usniisa.
An item symbolizing Buddha is a vajra club. Its mantra, a syllable symbolizing Buddha is 'bhruum'.
According to "Daishomyo Kichijobosatsu Setsujosaikyoryohorin" (Taishoshinshu Daizokyo No.966), the Buddha beams lights from pores, wears a Gobutsukan (crown with a design of five tathagata) and has hands that look like Shakyamuni.
According to the description, Shijokobuccho seems to be a bodhisattva form that wears ornaments, but a lot of its statues and images are in the form of tathagata. In the image kept in Daigoji Temple, it is a tathagata form holding a bowl and a shakujo (a priest's pewter staff) and flames are coming out from its head.
In the image kept as the main object of worship in Shorenin Temple in Kyoto, it is expressed as a mandala chart with a mantra 'bhruum' in the center of a white lotus flower that is surrounded by various Buddha. This mantra originally symbolizes Ichijikinrinbuccho, a deified mantra 'bhruum', and as Ichijikinrin and Shijoko are identified with each other, it is called Shijoko Nyorai in Shorenin Temple. The mantra drawn in the image represents the syllable 'bhruum,' indicating the close relationship between the usniisa and the belief in mantra.
Shijokobuccho is believed to win over evil deities in the heavenly bodies including navagraha (nine planet deities) with its light, and the sutra "Shosaimyokichijodarani" is known for its mantra. In the Tendai sect, Shijokobuccho is considered Buddhist prayers to protect against cataclysms and treated as the main object of worship.
As mentioned above, Shijokobuccho is identified with Ichijikinrinbuccho, where Shijoko is regarded as tathagata winning over deities in the heavenly bodies with its light and Ichijikinrin is regarded as tathagata decreeing the deities in the heavenly bodies.