Nissay Marunouchi Building, Office skyscraper in Marunouchi, Japan

The Nissay Marunouchi Building is a 160-metre tower completed in 2004, part of the Marunouchi OAZO complex facing Tokyo Station's north exit. Its pale grey facade is a tight grid of narrow vertical windows rising to a flat top edged with vertical fins, above a wider base with larger openings. Nikken Sekkei designed it with Mitsubishi Estate; floor area is 94,414 m².

The building was completed in 2004 as part of a major city development project called Marunouchi OAZO, which aimed to modernize Tokyo's financial district. It was one of several new towers that changed the face of central Tokyo in the 2000s.

The name OAZO stands for "Office & Amenity ZOne", linking Marunouchi (O) and Otemachi (O); it also echoes the Esperanto word oazo, meaning oasis. In the OO Hiroba square, named for connecting Maru and O, hangs a full-size ceramic-tile reproduction of Picasso's Guernica. The complex also holds the Maruzen Marunouchi main store and, until 2010, the JAXAi space centre.

The building sits just steps from Tokyo Station and connects easily to multiple subway lines below ground. Visitors can enter through several doors and have plenty of room to explore the public areas inside.

The OAZO name combines Marunouchi (O) and Otemachi (O) with AZ, for "Office & Amenity ZOne", and also echoes Esperanto oazo, "oasis". In the ○○ Hiroba plaza hangs a full-size ceramic-tile reproduction of Picasso's Guernica.