Just out of curiosity, are there any foreigners who are currently respected well-known manga artists? If not, that's not to say that your dream isn't likely, but I wouldn't put all your eggs in one basket. Without being too harsh, being a foreigner is probably going to close more doors than it'll open in your chosen profession.
Furthermore, don't just "try to get a grant or something" after going to teach English in Japan. Have a plan. Have a back-up plan. Make sure that your vague idea of what to do before and after you get there becomes a feasible plan, and if things don't go your way, it's not the end of the world. It'd be a good idea to find out if there are any scholarships that will let you go to this particular university, or if the university accomodates foreigners (or if there are any other possible schools). If not, you'd better take JimmySeal's advice and get crackin on learning the language. In fact, you should be doing that anyways. How else do you expect to function in a predominantly Japanese profession in Japanese Society?