To expand on my further post, one of the most popular console games in Japanese gaming history is
Dragon Quest, which some might remember playing on the NES by the name of Dragon Warrior. It's very much a console game take on D&D, down to the faux-medieval Europe and European style dragons.
As for the OP...what's your Japanese ability? I ask because just from a bit of Googling, I found a whole slew of gaming groups in Tokyo, and also Osaka (for [MENTION=6785986]Dargrimm[/MENTION]).
Here's a list of stores running Encounters -- R&R Station in Akihabara, and Reaching Moon in Osaka. Just in November was DAC (Dungeons & Dragons Annual Convention), Japan's biggest D&D con, held every year in Tokyo. This year they had 36 tables going.
Seriously, when I was looking for a game, I put ダンジョンズ&ドラゴンズ and 名古屋 into a search engine, and found a number of groups. I contacted one, introduced myself, and started playing monthly. If you're comfortable playing in Japanese, you have plenty of options, especially in Tokyo of all places. Where otaku gather, there shall D&D be found.