There are some style of drawing Mirokubosatsu, such as Mirokujyodohennsouzu or Mirokuraigeizu, this drawing is rather normal style, sitting on the round window to save people.
Mirokubosatsu is also called as Jihibosatsu, and is the first Bosatsu in any Buddhism stories. It is said that as a real existing person, as the server of Buddha, it had been taught by Buddha that it would definitely go to heaven after its die, and actually went to Tosotsuten and saved people. It is also said that 5,670 million years after Buddha died, it would come to a Baba world, the world of human being, and would save the people whom Buddha wouldn't help yet.
Thus, it had been faithful from early days in Japan, there is a drawing of Mirokubosatsushiyuizou kept in Kouryuji in Kyoto, and it formed as Hankashiyuikei in most of drawings. The Bosatsuzo of Syourinan is also one of them.
It is especially valuable that it has never been repaired since it was drawn in Kamakura period. However, it is pity that the gold lines for eyes and nose are fading out as time goes by. It is one of the few silk coloured examples of national cultural property as Takayamadera and Daigoji.
Explanation 
Mantokuji
