How should a student with no research background write a research proposal?
I don't know how to continue.


Well, there's a lot to do, actually. For example, you can structure your research proposal in the following sections (other points can be added):


Introduction and background information. Here you should clearly state the goal(s) of your research and give supporting information. For example, since you claim that multiculturalism is denied in Japan, in this first section you shall report this claim and provide supporting references; then, you shall explain that this phenomenon is not well studied and why it would be a good thing to investigate it.
Methodology. How do you plan to carry out your research? Anonymous questionnaires? Interviewing people? What kind of questions do you want to ask? How do you choose the population sample? How do you plan to carry out the interviews or distribute the questionnaires? Especially, whatever methodology you choose, explain clearly why the chosen methodology is suitable for reaching the goals of your research. 
Data analysis. Here you have to describe in which way you plan to analyze the data you have collected.
Schedule. Subdivide your research in different tasks and describe the time allotted to each one (Gantt charts are common these days).
Scientific outcome. Original research is typically published on journals and presented at conferences. Can you name a journal and/or a conference suitable for your research topic? Can you think of other possible outcomes? For example, if the subject of your investigation constitute a social issue, can you think of writing a recommendation suggesting ways to improve the situation?
Possible issues. Describe what can go wrong in your plans and how you intend to mitigate possible problems (e.g. people not answering to questionnaires).
Resources and costs. Every kind of research needs money and resources. For example, if you plan to realize an online questionnaire you might need to hire a developer. So, try to figure out what can be the amount of money needed to make your research and write down a small budget. 


Edit: I've added a couple of points. That said, good luck!