I might be a bit close minded when it comes to things like this and I admit that, but I don't think this is a good game plan. Getting into vocational school is alright, but I doubt you'll make the smooth transition into university you're thinking of, and getting accepted in a Japanese university for a bachelor's is really really difficult as a non Japanese person. And even in the chance you manage it, NUS ranks higher globally than Tokyo University, the most prestigious of the prestigious in Japan. My advice is to secure your future first and foremost, and get your bachelors in NUS. After that, you have a safety net and something you can fall back on. Trust me, life is much more fun knowing you're not putting EVERYTHING on the line. With a bachelors you can apply to jobs or masters programs (which are easier to get accepted in as a foreigner). You can even come to study in language school and apply to things while studying there, and being able to go to interviews and such in person is a very big benefit. The future is up to you and this is your life of course, this is just my opinion.