I've been to Japan a few times - I wouldn't recommend you try and take weed over there through customs. You'll have a blast with the nightlife options available in Tokyo, it will completely blow your mind.
Even in the electronic music scene in Tokyo, crazy as it is, you will not find drugs of any description, including weed, to be
easily available. You will have a language barrier so that won't help - the younger generation in Japan do speak okay english (occasionally LOL) but they are often shy to use it regardless.
Unless you have a contact in Japan who can sort you weed, I say forget about it and if you happen to stumble upon it (which you probably won't), then it's a bonus. If you walk up to a Japanese person and say "you wouldn't happen to have any weed for sale would you?", they'll probably look at you as if you're from another planet... chances are they'll have no idea what you're talking about.
And that goes with anything you want to ask to by the way. Good luck getting back to your hotel in a taxi after a big night if you haven't got a map readily available.
Not trying to scare you off Japan - I personally think it's the most amazing place in the world. The Japanese are probably the most polite people you will ever have the pleasure of meeting. They will go out of their way to help you, however they can. They will walk 20 minutes out of there way to show you where a shop or restaurant is (just remember your map), they will chase you around the street if you accidently leave 5 yen (fuck all) at a restaurant. They are wonderful characters.
Also, I wouldn't wait until April if you're after the snow, although there is often still some there. April is, however a wonderful time for Cherry Blossoms (Spring) which livens up the streets and there's always lots of festivals on.
Late December - early March is good for the snow, but best bet is Late Jan or February. We went early March to Hakuba this year and it was great, snowed the whole time, but it's definitely getting towards the end of the season at that time.
I suggest you learn some basic Japanese before you go. Try the 'pimsleur' audio disks for conversational Japanese - you can grab these off amazon.com. EVERYONE wishes they had learned some Japanese prior to going there, trust me on this.
If you want tips on places to go for nightlife, must see destinations, or anything else let me know
