Nothing to add than pictures. It looks like has changed since the initial facade one can see in the Kuma site.
Here below the actual look.
“Although Japan’s Building Standard Law prohibits the use of wood on the exterior walls of buildings in large urban areas we were able to obtain special permission by installing a drencher on the outside wall.”
In this link, very nice professional pictures of the interior space.
In this link an interview of Kuma about how he likes some F.Wright concepts.
BEside the wood feeling that he claimed to want to restore in that tree respect (the zelkowa trees along both sides of the street) the other word that goes to my mind was “Marble”. Luxury marble. Thus immediately I have thought of his work for L.Vuitton in Osaka which is a remarkable apical achievement in contemporary architecture and…yes it just the year after. So those interior walls just few inches from the facade showing marble natural grain were maybe a sort of basic idea of what came the year after.