i would appreciate a fast answer since i only have a few days before the funeral.

I'm not sure you'll be able to find suit rentals, I was only able to find them for weddings, and the ones I saw were very expensive.

By the way, I don't even know if I'm going yet. I have only six months with my girlfriend and I'm not that close to her family yet. Since this is a family affair, she told me she was going to ask her father if it was ok for me to go. I asked her yesterday and she avoided the question. She hasn't said anything yet so I think her father didn't agree very much hehe

But that's ok with me. I understand it's family business so I might as well stay out of this for now.

So I'd check out the suit shop options first, as it is only a few thousand yen more, and they may be able to tailor it in time. Even if they can't tailor in time, neither can Muji, so you can always keep that as a backup.

Also, your gf's grandfather's funeral is a time to be as formal as possible. All the men will be in proper black suits and you wouldn't want any reason to stand out more than you already do just by attending.

BTW, I'd confirm that you're even going first. As you metioned, check with the family, and make sure its ok with them and not just your gf. Also, are you aware of the procedures for a Japanese funeral. The family sits up front seperated by gender, so likely you will be sitting alone with the regular attendees and will not be with your gf during the service. Make sure you are briefed on what to expect as it is very different from a western funeral, and could be quite an uncomfortable experience to go in unprepared.

I thank you for your time to help me with the clothes and show me the ethic codes in a Japanese funeral. It was very different indeed. Your links helped a lot because my girlfriend didn't explain a thing to me.

Anyway, I'm very glad with the results. Actually, before that, my girlfriend had asked me to write a message for her grandfather in the back of a picture of us. She wanted to put it inside the coffin with the ashes of her grandfather . I put so much effort into that message as I was trying to use really polite japanese and say some good words (it took me hours). My girlfriend was impressed with my words and was very thankful. I thought that was about it, but then, the message was read in public during the funeral and everyone was astonished to see that a gaijin could actually write good things in japanese. After that many family members wanted to meet "the gaijin boyfriend".
I'm happy because I think I left a good impression and this could be the beginning of a good relationship with my gf's family.

well, just a story I wanted to share with you guys.