In the Jodo (Pure Land) sect of Buddhism, Raigo means Amida Nyorai (Amitabha Tathagata), who is riding on the colorful clouds together with various bosatsu and tennin (heavenly beings), coming to see a person who is about to die in order to take him or her to the heavens, and who is served by Kannon Bosatsu (Kannon Buddhisattva) and Seishi Bosatsu on the side.
Also, the picture painted in the above situation is called raigo-zu (image of the descent of Amida Buddha).
The belief of Amida 'if someone believes in Amida Nyorai, he will come and guide the person to the heavens at the time of death' became popular in the middle Heian period, and many raigo-zu were painted. Kannon Bosatsu stands atop the clouds with his palms placed together. Shisei Bosatsu holds a lotus pedestal (a pedestal with a lotus shape).
The raigo-zu is based on the "Kanmuryoju-kyo sutra "('The Sutra of Visualization of the Buddha of Measureless Life,' meaning Amida), as is seen in Taima mandala, since the kuhon ojo (nine levels of birth in the Pure Land) from jobon josho to gebon gesho, the way raigo is painted, varies with each level of birth in the Pure Land.
The raigo-zu, a national treasure kept in Chion-Temple, called 'Hayaraigo,' is officially called 'Amida Nijugo Bosatsu Raigozu' (Descent of Amida and Twenty-Five Attendants); it has a picture of Amida Nyorai coming over the mountain to take some people into the heavens which is explained in "Kangyo" (Meditation Sutra).
Amida Coming over the Mountains' is one of the raigo-zu which is known as a collection of books of Zenrin-ji Temple (Kyoto City) (National Treasure), and has a large exaggerated picture of Amida Nyorai coming over the mountains to collect someone.
Amida Sanzon-zo (the image of Amida Triad) (a National Treasure), which is the honzon of Sanzenin Temple, isn't the picture but a statue, and it very clearly shows how Sanzon comes to collect someone; additionally, it is well known as kyoji (attendant figures) of two Bosatsu sitting in the Japanese style instead of being cross-legged.
Originally it had a picture in the Jodo-shinko (the Pure Land faith) style, since it is of the Jodo-shinko school, but it has content related to all other religions.