It is a souvenir shop where it is located on 1st floor of RADIOKAIKAN.
It is easy to go into the shop sicne the shop is right in front of the entrance.
There are so many souvenirs of Tokyo here, but especially they have a lot of "AKIBA" souvenirs! There are souvenirs collaborated with anime and game ones which I think very interesting even just watching them. Because there are variety of printed cookies, it is a perfect souvenir for your friend who love anime. I got myself a Pikachu candy which package is like monster ball (the case and candy are both adorable!).