Not really a answer to your question, but...
He could extend his tourist visa, especially if he has a good reason. i have done it once. he will then get another 15 days. the problem with this is that he will not know whether he will really get the extension at the time of entry, or when buying the ticket for that matter.
the most obvious recommendation would of course be to contact the JP embassy in his country, or contact the immigration office in Japan. Unfortunately they do not yet have e-mail service in english (they didn't have it two years ago), but perhaps his partner could take care of that.
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