Most recruiters in Japan are looking for candidates whose background and skills match the ones they think a client will want.
If you contact a recruiter or a recruiter contacts you, they are looking to understand if you fit that profile. Depending on what area they specialize in (industry like IT, Finance, or Life Sciences) and the level of the candidate they handle (Junior, Mid-level, and Senior), you can try to tell if you are in their target area.
One example of how a Recruiter explains what they do
This is a little long video from an Executive Search firm specializing in Senior roles, but it does give a generally good overview of the search process Thinking of becoming a Recruitment Consultant? See this video to check out one company's pitch
So by sending a resume/cv to the recruiter and having a phone interview, you can set the stage for how they will view your strengths and weaknesses. Typically, a junior researcher will contact you to do an initial screening, and then schedule an inperson interview with one or more recruiters. Or you go to their office, have a language or skills test, and then review some sample opportunities.
Ambition, a look at a boutique recruitment consultancy
You should see if the opportunities they show you match your expectations, or what your career has been. If it involves a new field or skill, can you do the job and are you interested? If you get an interview with the hiring manager, can you reasonably explain how your background and skills help them to succeed? Hays Japan Recruiter talks about her career
Getting feedback on the interview process is really helpful, but it is not always the focus of recruiters. You can judge a recruiter by the aftercare they provide, in that, if you tell them how you think the interview went, along with types of questions and focus, then the recruiter should give you feedback on the company's reaction to the interview.
Sometimes the recruiter doesn't get that from the hiring company if the interview wasn't successful, and there are no specific feedback points that they share; but responsiveness to your questions can help you to decide when to focus on other job opportunities.