I was a flight attendant for one of the large airlines in Japan and never experienced drunk pilots or colleagues in the 2.5 years of flying long-haul. Although paradoxbox is completely right about drinking culture of Japanese business men and office workers (in the worst case, you find them lying around the streets and subway stations, unable to go home and just returning back to work in the morning) but all the crew members I worked with did the exact opposite. It is all about "fitting in" in Japan. You drink with your colleagues to fit into the office culture, but you do not drink more than a glass at dinner to fit in with your pilot cohort. So they can very much behave responsibly. This individual must have had a personal issue to break the rules.
The Japanese culture definitely distributes the responsibility amongst the colleagues, so presumably the other two pilots knew that this guy is intoxicated and would have set him to crew rest for the duration of the flight without reporting it, thus covering for him but also themselves. (Same for cabin crew who might get very ill shortly before a flight back home)
Now that it became a big public issue, the other pilots are probably going to be held responsible for not better supervising their "younger" colleague. I agree that heavy and repeated drinking is an illness, but from my experience this is a minority within the cockpit and cabin crew. Japanese crew proud and overly meticulous in their approach to work and my time felt very much like I was in the military - so strict and diligent! Hai!