Shizuoka Press and Broadcasting Center (1967) by Kenzo Tange. This 12 story building was the first realization of Metabolism. Thirteen individual office modules are connected in clusters to a central core.
Like the Nakagin, the design allows for additional modules to be "plugged in".
Source: Class Connection
The Metabolist idea of the structure growing, reproducing, and transforming in response to the environment has yet to happen for Shizuoka. No modules have been added since it opened in 1967. I'm still optimistic.