advice on marketing in Japan?

Here are some things off the top of my head (they are all very common sense):

Do research online looking for music and lifestyle websites (that are appropriate to your style of music) targeting Japan and contact them.

Send your music to Japanese magazines.

Find companies that market music to japan and contact them.

Find a marketing company that has japan contacts.

Get a Japanese record deal.

Become friends with people who live in Japan who can help you.