I would think it must be a bit easier for Mervin to get Japanese citizenship, if only both Mervin and JSF will go all for it and plead the government for a special treatment to relax (=lower) its requirements in his case.
I remember Rugby National team had 10 players who were originally non Japanese to compete for the Rugby World Cup 2011 in New Zealand, and five of them were registered as the naturalized Japanese citizens.
Other example I can think of is Sumo. We have many Sumo wrestlers who were originally born in Mongolia, and are now officially naturalized Japanese. I do not believe all of these rugby players and sumo wrestlers actually filled in all the requirements, such as to speak perfect Japanese and/or write decent Japanese. With the strong back-up by its federation, there must be some exceptions applicable for a sport, maybe?
Out of the 5 rugby players, one 1 was a rare exception in that it took him just over a year. The rest took much, much longer. They also live and train in Japan, which Tran does'nt do.
There's a reason why Japan is one of the most homogenous nations in the world and citizenship is very difficult to obtain. Tran doesn't speak Japanese and has made NO EFFORT to integrate himself into Japanese society. He doesn't deserve citizenship.
Also, I'm not completely sold on T/T as olympic medal contenders so I wouldn't approve of citizenship based on some offchance they may medal if other teams do poorly.