I actually writing this post and I would love to go back there! It was the first time in more than twenty days that somebody stops me speaking english for offering me an help to find a place. I was obviously holding a Tokyo map and I was fumbling through the pages.
The library was spreaded among three buildings if I am recalling well. All were connected by a unifying design, based on a little joint game.
Precisely this one below in the picture.
Here some more shots.