If I met you on the road somewhere and you asked this and I only had a few minutes to impart a few ideas I would narrow it down according to the idea of First Principles. Above all else... what is that one thing that is the most essential critical thing for Japanese? What do the Japanese value above all else, irrespective of suggestions you'll hear like loyalty... cultural background, race, language ability, likability, social status, popularity etc.... I'd have to say... excellence.
The Japanese are in awe of excellence, the pursuit of excellence etc... they are positively neurotic when it comes to the idea of pursuing an endeavor to the end of its achievable level of excellence. If you are able to achieve excellence in your job, you will earn so much goodwill, that everything else will be smooth sailing.
My dad and I were talking about his stint as a consultant for a major Japanese industrial electronics giant, supposedly the cutting edge forte of Japanese excellence... but he discovered they were completely clueless. He didn't speak a word Japanese, didn't socialize much with any of the executives, didn't imbibe... did nothing the Japanese would really approve of in terms of how they approach their work culture... but... he could outwork them... out-think them and most importantly... out-innovate them. He finished a one-year contract in 6 months, got along swingingly with everyone and had fond memories of the experience.
Be excellent. The rest will take care of itself.