Could it not be Black-eared Kite? It would not stand out in Japan at least, I'd say.
I understand the two (sub)species overlap in central/east Eurasia, but this one looks quite ok for lineatus even.
compare with all Black-eareds in Japan:
Observations*
*I don't think European type Black Kite has been recorded in East Asia, correct me if I'm wrong.
please let's not turn this thread into toxic waste....thanks!
cheers,
Gerben