Studying in Japan

Hello everybody, a friend of mine wants to study in Japan for her masters degree. She is from Montenegro and has some questions about applying.
She wants to apply Meiji, Sophia and University of Tokyo. Shes a really good student but has questions about applying. What is MEXT grading system and how does she convert her grades into it? Are there any specific things she needs to do to apply to either of these universities that arent really know? If anyone here has experience with this topic what did you do?