This is a strikingly black and white male with a long head tassel, but females are mostly brown with only a rudimentary tuft. The broad black bill tip extending well beyond the nail is a useful identification feature. Japan is near the easternmost end of their breeding range which extends across northern Eurasia. Canon SX60 HS PowerShot.
References:
Azzi, M. and R. Garrison 2012. "Aythya fuligula" (On-line), Animal Diversity Web. Accessed October 01, 2018 at http://animaldiversity.org/accounts/Aythya_fuligula/
Carboneras, C. & Kirwan, G.M. (2018). Tufted Duck (Aythya fuligula). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/52910 on 1 October 2018).
Madge, S. & Burn, H. (1988) Waterfowl. An identification guide to the ducks, geese and swans of the world. Houghton Mufflin, Boston.
Todd, F. (1979). Waterfowl. Ducks, Geese & Swans of the World. Sea World, San Diego.