The Kajima Akasaka Annex was planned as part of a relocation of the head office of the general contractor Kajima Corporation. The design was conceived to be in harmony with the existing KI Building, with an exterior that integrates the lower office portion with the upper six floors of required residential units. The smoked glass used for the exterior is the same type of heat-absorbent glass in the KI Building, with multi-layered Low-E (low emissivity) coated glass (current glass technology). The width of the mullions is also the same as the KI Building at 350 millimeters (13.8 inches), keeping the design in harmony. The proportions of the delicate frame of exposed reinforced concrete, together with the smoked glass, make for a striking expression.