MacArthur was supposed to be lenient toward the Japanese? (an actual question).
Yes. Read some history. MacArthur was more lenient than the Japanese had any right to expect.
He was given a free hand, and turned out to have been far more generous and conciliatory that anyone thought would be the case. In August 1945, 90% of the American people wouldn't have objected to mass sterilization of the Japanese people, if not outright elimination. That we two nations have overcome all that in sixty years' time is largely attributable to MacArthur's occupation policies, which he mostly devised himself.