The bonji of the sutra box is the letter « A » in ancient indian writing, siddham. It is the first lettre of the alphabet, and so represents the origin of everything. But most of all, in sanskrit, « A » has a deprivation sense, just as the deprivative « A » in Greek. It symbolizes the buddhist conception whereby every existing thing is originally « unborn » (Honpushô 本不生.sanscrit : âdyanutpâda).