If I remember well, Takumi plays piano in Dir en grey's unplugged tracks on DSS...
Edit: Well, it seems he also did tour with Dir en grey doing their manipulation and does programming for their albums. And Mika has worked with some Dir en grey videos(single dvds and stuff like that) as he has an audio visual company called Unravel Films.
takumi's blog http://ameblo.jp/takumixofficial/