Go grab it on the eShop
Brain Training (also known as Brain Age) was the first DS game to hit the Wii U in Japan. Now European Wii U owners can go download it for free. Without any sort of fanfare, Nintendo has released the game to the eShop.
It looks like you'll only be able to nab it until July 10th for free, so go do pick it up soon before you forget. Hopefully it'll arrive on the North American eShop in the near future -- although, this would have been a great "download it now for free!" E3 announcement.