In modern times, not a small number of nations has adopted the prinicple of separation of religion and politics for its constitution except those of Islamic nations. For the japanese, this principle is not novelty at all.
We can find in the Japnese many eras when the separation of Religion and Politics or of Authority and Power had substantialized in the dual system composed of the Tennou and regents, ex-Tennous, and especially Shoguns who initiated fuedal governmets distant from the Capital city Kyoto.
Syotoku-Taisshi, who is famous as a hero who rejected bravely to subordinate Sui that was one of ancient chinese dynasties and to be circumscribed within its feudal or imperial ismic international order, was also a regent for Suiiko-Tennou.