Therefore, historical materials to be support the theory are limited to kiki (the Kojiki and Nihonshoki) or unrelated articles which often appeared in history books of China or Korea, and to few facts regarding the Kyushu era (it has not been proven that itsunengo [era name really existed and taken out of official history] corresponds to the Kyushu era) or Dazai-fu.
したがって説の論拠となる史料は、記紀や中国や韓国の歴史書等に散見される間接的な記事、九州年号（逸年号が九州年号である証明は無い）や大宰府など僅かに残されたものに止まっている。