Boeing 747-400 (domestic, no winglets) (JA8961)

Why the aircraft is it watered?

I'm not sure why this one was given a water salute, but a plane will often be given the salute when the pilot is on his last flight before retiring. This one could have been for that reason or maybe because the aircraft was being retired.

Most likely because the airplane was being retired because as of 4/14 or 15 there is now no 747s in Japan because ANA retired there last.