Getting married in Japan

I'm not sure if this is the right place to post this so sorry if I'm wrong.
I've been in an online relationship with a Japanese man for more than 2 years, we talk daily since the first day and I'm going to Japan soon so we will finally meet face to face.
I'll be there for three months (more if it's possible) and we were thinking about getting married if things go fine once we date some months for real.
Please, don't say it's crazy, I already know it's crazy to marry someone you only know online after dating just few months, we will not do it unless we're 100% sure, so right now, I only want to ask for information just to be ready in case we decide to do it.

My doubts are... what documents will I need to get married in Japan? Do I have to get those documents in my country?
I guess I will have to apply for a spousal visa after getting married... How much time does it take to get it? Will I have any problem to get it since we won't date for a long time? In case there is any problem, will it help to tell them we met online first and we've been talking for years?
And last question, if we marry and I apply for a spousal visa, do I have to go back to my country while I wait for it? Cause I go to Japan as a tourist so I can only be there legally for three months.

The documents that are important to get married varies depending on country where you come from. In my case (Poland) it is:
-birth certificate
-the certificate of eligibility of getting married abroad

Both documents have to be translated by embassy into Japanese. Note, that the second one is valid only for 3 months!
It is better to confirm at the city hall you are planning to deliver the documents to.

For spousal visa you will need to prove that your marriage is real by showing photos of you two while dating, phone bills, e-mails, messages etc. Also, you need to write your detailed relationship history. How you two met etc.
You will need to wait 1 to 3 months for spousal visa.

I hope it helps! :)

Where are you from?

It may vary a bit by country, but for US citizens getting married in Japan, you need to have a document from the US consulate saying you are currently unmarried and are free to marry in Japan. It is pretty easy to get, but you might need to make an appointment a bit in advance since spots can fill pretty quickly. You can make the appointment online, and there are a number around the country depending on where you are staying.

With this document (and the translation, which any Japanese speaker can do), you can legally get married here.

Once you have signed the marriage paperwork at your local city hall and are entered under your husband's koseki, you can bring those papers plus a number of other required documents to immigration to apply for your spousal visa. If you apply and you are on a tourist visa, immigration should give you an extension/permission to stay for about 2 months from when you go in, but the length of time may vary.

The time it takes to get your spousal visa really depends on a lot of factors. Mine took a week, some people wait 3 months. I think it has to do with a number of factors including which immigration office you go to, how long you have been together, and your citizenship among other things.

As long as your visa/the extension you're given while waiting for your visa is valid, you don't have to leave. However if you still haven't heard when your time is up, you will need to either apply for another extension at immigration (which may or may not be granted), or leave and then come back again.

Oh, and for my spousal visa application, I just brought in a few pictures of the two of us and that was enough proof. I didn't have to bother with emails/phone bills/other junk. This too may vary by country and experience however.

As scarreddragon said,
a lot depends on your home country. Same for spousal visa. Americans can get it easier than e.g. Filipinos since there is not many cases of fake marriages.

Thanks for your answers!

I am from Spain.
Correct me if I'm wrong, please, but do I have to get the documents I need in the Spanish embassy in Japan?

I hope someone else will chime in and correct me where I am wrong, but I believe that it doesn't matter whether you get the documents in Spain, or at the Spanish Embassy in Japan, since they are the same. Most people go to the embassy because they are in Japan at the time, but you can always get the documents in advance.

However, please heed what himcia said about the 3 month validity... some documents expire! So don't get one if it has a time limit on it. You can wait until you are in Japan for anything you need!

(Again, I'm American, so I'm only speaking on knowledge of the US and US consulate. I think it would be good for you to call the Japanese Embassy in Spain to confirm any questions you have too!)

here is the detailed procedure with a Japanese and a Spain nationals.
the example is in the reverse, i.e. a wife is Japanese. but the procedure should be the same.
since the website is in Japanese, you may tell him this site.
http://www11.plala.or.jp/LUNARES/casamiento.htm
you need to bring the documents from Spain, CERTIFICADO DE EMPADRONAMIENTO and CERTIFICADO LITERAL DE NACIMIENTO.

In case of Poland, you need to have the birth certificate sent from your home country (a family member can get it for you). Then based on that you can "get" the marriage eligibility certificate via Polish Embassy in Japan.
However, it is not that easy. They will apply for the certificate to the city hall in Poland and it will be sent to your representative (family member) in Poland. Then the family member can send it to you to Japan. It takes quite a lot time and hey, you still need a translation to Japanese! (somebody said everyone can do it, but I was told int he city hall that it must be done through the embassy...) I hope Spanish embassy works better....

...if not, it is much much better to bring it with you and just be careful about validity period.

Okay, thank you very much for your answers!