The Nishi-shinjuku skyscraper business district was Tokyo's first major foray into building skyscrapers with the first appearing in the 1970s with Keio Plaza Inter-Continental. Kenzo Tange's Tokyo Metropolitan Government Building being the current latest. Tower I was also the tallest building in Japan at this time.
Progress continues in Nishi-shinjuku and in West Shinjuku which is heading away from the city center and has the site of the coming Nishi-shinjuku 3-Chome redevelopment with plans for what will be 3 of the 4 tallest buildings in Japan.
Nishi Shinjuku is a seismically stable area that escaped the last earthquake with nary a scratch, is Tokyo's skyscraper district featuring (among others) the gargantuan Tokyo Metropolitan Government Offices. Microsoft has a major office (with an imposing sign) just across the street from the south exit of the station.
(reference: Wikipedia, Wikitravel)