At the beginning of the Kencho era (1249), ‘Old Buddha’ Daikaku was invited from Kyoto by the shogun Tokiyori to spread Zen in the East of Japan. Some priests and laymen of other sects were not at all pleased at this, and out of jealousy spread it around that the teacher was a spy sent to Japan by the Mongols; gradually more and more people began to believe it. At the time the Mongols were in fact sending emissaries to Japan, and the shogun’s government, misled by the campaign of rumours, transferred the teacher to Koshu. He was not the least disturbed, but gladly followed the karma which led him away.
Some officials there who were firm believers in repetition of the formula of the Lotus, or in recitation of the name of Amida, one day came to him and said: ‘The Heart Sutra which is read in the Zen tradition is long and difficult to read, whereas Nichiren teaches the formula of the Lotus which has only seven syllables, and Ippen teaches repetition of the name of Amida, which is only six. The Zen Sutra is much longer, and it is difficult to get through it.’
The teacher listened to all this and said: ‘What would a follower of Zen want with a long text? If you want to recite the Zen sutra, do it with one word. It is the six- and seven-word ones which are too long.’
Master Setsuo used to present his pupils with this story as the riddle of Daikaku’s One-word Sutra. He would say to them: ‘The golden-faced teacher (Buddha), it is said, in all his forty-nine years of preaching never uttered a single word. But our Old Buddha (Daikaku) declares one word to lead the people to salvation. What is that word, say! What is that one word? If you cannot find it your whole life will be spent entangled in creepers in a dark cave. If you can say it, with that leap of realization you will pervade heaven and earth.’
(Imai’s note: Those who were set this riddle over the years tried the word ‘heart’, and the word ‘Buddha’, or ‘dharma’, ‘God’, ‘mantra’, but none of them hit it. When the pearly sweat runs down the body, coming and going for the interviews with the teacher, the one word will be met directly.)
This became a koan in Kamakura Zen at the interviews of Setsuo, the 151st master at Kenchoji.