It is rumoured that beneath the Kyoto old imperial palace lay the huge underground ‘human farm’, where shinto priests fed the slave race for the ritual sacrifice.
Greater part of these ‘cattle humans’ are criminal Japanese, or foreign captives, or descendants of such people. On the other hand, the farm is said to have propagated offspring of the archaic humans who are commonly believed to be extinct like Neanderthals or Piltdown men. Since the birth of the civilisation (or perhaps, since several centuries before that), Japanese imperial priests propagated and fed those cattle humans there, merely to slay them for the sacrifice for the emperor.
And It is also the fact that, horrifically enough, such a slave city is gossipped to exist still now in the dim and bloody underground space below the current palace in Tokyo.