Kōjiro Shindō is a highly-skilled negotiator working for the Ministry of Foreign Affairs. As his plane at Haneda airport prepares to take off, a huge mysterious cube appears from the sky. 'It' expands rapidly, and absorbs the passenger plane and its 252 passengers. The cube's name is "Kado". A strange being called Yaha-kui zaShunina appears from within Kado and tries to make contact with humanity. Shindō, who was been absorbed by Kado, ends up taking on the role of mediator between Yaha-kui zaShunina and humanity. The Japanese government sends its own negotiator, Saraka Tsukai.