Japanese Paradise Flycatcher (Terpsiphone atrocaudata) サンコウチョウ
A male Japanese Paradise Flycatcher in breeding plumage. The blue rings stick out during breading season.
The male Japanese Paradise Flycatchers also have very long tails during breeding season.
A male Japanese Paradise Flycatcher singing.
A female Japanese Paradise Flycatcher has a black back.
I think that this is a juvenile Japanese Paradise Flycatcher.