Japanese airlines don't check your ID for check-in or for boarding. If you have a friend in Japan and if you look Japanese/Asian enough, then .... (Some people seems to be abusing this for those 10,000 yen day tickets that allows you to take as many flights a day, selling segments.)
From BKK, NH has 45-day valid Y tickets that allows connections to most cities in Japan, Kagoshima included. Domestic segments are booked under Y. So you get 100% credit for Star Alliance programs. NH's AMC nets double Platinum points as per regulation for Y domestic tickets.