It is interesting to know that the year 784 was the year of the Kasshi kakurei (the first year of the sixty-year cycle in Chinese calendar when changes are often said to happen), and that Emperor Kanmu was a direct descendant of Emperor Tenchi, not of Emperor Tenmu.
784年は甲子革令の年であり、桓武帝は天武天皇系から天智天皇系の天皇であったことも興味深い。