Hello Slink:
Firstly, good luck with your plans (no sarcasm). Let me touch on some of the points that came up.
Language proficiency
In Japan, at least JPLT 2 is required for undergraduate admissions (it may vary by university or program and some places may require N1).
The fact that there are international students at your school means that they scored around 550 on TOEFL (maybe as low as 520- depending on your school) which relatively speaking is, IMO, a bit higher than JPLT N2. Like TOELF, JPLT has no speaking component. That means your speaking ability has no impact on your chance of meeting that Japanese language requirements. Bottom line: you must pass level 2. The next tex is not until July (
JLPT Japanese-Language Proficiency Test but if you want to get an idea of where you stand, you could try the J-test (
J.TEST実用日本語検定 | TEST OF PRACTICAL JAPANESE The key to passing is the ability to recognize (well enough to read and understand- but it doesn't matter if you know how to pronounce what you can read) Japanese
kanji.
Transferring Universities: 編入学試験
Actually, it is not all that rare, among national universities (I do not know about private universities). If you google this :編入学試験 plus the name of the university you want to attend, you can find the conditions. It is quite common for students that failed the entrance exam at their first choice of university with a high GPA at their second choice (where they now attend) to take transfer exams (usually August or Sept). I is usually, a written test(s) and interview.
However, an additional difficulty you will have is the recognition of your HOME university credits. Even if your university has an university level academic agreement (MOA/MOU/AOC, etc.), it is unlikely that they have a credit exchange and recognition system in place. These can take a very long time to set up (because of university and MEXT regulations and requirements, and the regs and requirements from the other university and gov't organization - perhaps regional accreditation body in the US - I DO NOT KNOW).
It is possible (but I do not know if it is these days) that you could be admitted through a special admission process (I have heard of 1 case - anecdotally - years ago). Based upon what I know, at least it would require the strong support of a prof or profs before hand, probably approval of at least 4 committees (International, Admissions, Curriculum, Internal management) the department, the faculty and the dean. So in short, IMO, unless there is already a system in place your chances are very slim of being able to do this. But do not let this discourage you from investigating on your own and checking with universities directly. After all, this is just an Internet forum and you need to check things out yourself.
My Unsolicited Advice
If you want to come to Japan to study, I would suggest that you finish your undergraduate degree and consider graduate studies in Japan. Japan is trying to increase the number of international students (non-Japanese) studying in Japan and there are many options at the masters level. There are also many scholarship chances (a government scholarship will include point to point airfare, tuition wavier and about 140,000 jpy living stipend), as well as university scholarships and other scholarships that you can apply for upon arrival.
You can also study graduate programs in English (or Japanese).
Requirements:
Program conducted in English: To improve your chances for admission you should have passed some JPLT tests (higher is better)
Program conducted in Japanese: At least N2 (depends on institution) but even at N1 you will struggle.
Minimum GPA 2.3 on a 3.0 scale. For more information, ask the Unversity you are applying for.
4 year Bachelor degree from recognized (e.g. accredited) university
Research proposal
Hope this helps