A guarantor (保証人hoshonin) is required for various types of contracts in Japan and especially for housing. When I first came to Japan and made my first housing contract I thought maybe it was because I was a foreigner that I was being asked to have a Japanese native vouch for me. But as it turns out, many Japanese also need guarantors, and sometimes it can be hard to find someone because people do not understand what it means or how much risk is potentially involved.
In fact, it is such a big concern nowadays that guarantor companies (保証人会社 hoshonin gaisha) have been increasing in Japan. I was actually joking around with one of my friends the other day and I teased him, that guarantor companies is a good business because of the increase of foreigners in Japan. He replied, my daughter needed a guarantor, but I couldn`t do it. That`s ok though, her boyfriend was able to help.
Nowadays, most the companies I deal with do not require Japanese citizens to be the guarantor, but some companies still do. And because you do take on financial liability (essentially you are saying if the tenant has outstanding debt or legal obligation to a company you are agreeing to be legally liable) it can be a hurdle.
Guarantor Companies
Although guarantor companies do exist they may be expensive. For example for a rental contract a company may charge half a months rent and sometimes an additional annual fee. This may be the best option in some cases though. one famous example is Nihon Saftey.
Getting a Guarantor
For some foreigners, the best option may be to ask their company, school, or visa sponsor. I did once have a teacher of mine sign a contract with me now that I think about it. It may have been for a job, because I was living in a house that did not require a guarantor. But anybody who is paying you or offering you a visa, already has financial interest in your success and would be a likely candidate for a guarantor
Another option is to ask a friend. Especially if the company does not require a Japanese guarantor, your guarantor will likely only be required to have a hanko or ability to sign a contract in Japan.