I'm not sure what exactly it is , seems like a controller .
http://akihabarashop.jp/images/DreamsPreOrderInfo.jpg
* Size of PCB: 50 x 40 millimeter.
* PCB has common ground.
* VMU connector on PCB, brand new, not desoldered from older pad.
* 4 meter long Dreamcast controller cable is included.
* No soldering required.
Source and the rest info :
http://www.akihabarashop.jp