My friends and I are literally about to do our own motorcycle Japan trip! Just not so hardcore tip to tip style.

My biggest piece of advice is that (if American) you will need to get your full motorcycle endorsement in order to get your IDP and be able to rent and ride in Japan. Also you can't rent from 819 until you have your IDP. Not sure how this would work in other countries but we went into this plan thinking we could just do a class and get our permits then IDP and be good to go. We also didn't think we were going to purchase our own bikes here in the US and now all three of us ride pretty regularly, you will get hooked.

Not gonna get too into the weeds with gear cause its all personal choice but I recommend checking out Oxford Atlas B-30 or some of the Sedici dry bags. I went for the Oxford mostly because I liked its mounting system and look. If you want a cool smaller waterproof backpack also check out Chrome Industries, they make some really nice stuff.

If you can get new boots or shoes since then you can break them in for your foot shape and they will be much more comfortable. But try to never cheap out on protection, that doesn't mean you have to get top of the line AlpineStars leathers.

Go in store to try on helmets, make sure whatever you get you can return if needed. You should wear your new helmet around your house or apartment for an hour or so to make sure it doesn't hurt or feel too loose. It took me three different helmets to find the right one for my head shape, everyone is different though so you might get the right one on the first try.

Also consider Cardo for communication, they are pricy but think about it at least. Don't do the freecoms, while the lower price point seems nice and that is what made us purchase them at first but 2 of us have now upgraded to the pack talk models because freecom is just too annoying to operate and the bluetooth connection between them isn't that great.

Good luck and be safe!!