The story takes place over a 24 hour period. In the southernmost part of Japan, 20 fishing boats of an unknown nationality suddenly fire upon and occupy parts of the Hateruma archipelago. Members of the Japan Coast Guard are detained. Under the extremely tense situation, the Japanese government sends Aircraft Carrier Ibuki and an escort fleet to the area. Ryota Akitsu is the captain of the Aircraft Carrier Ibuki and Toshiya Niinami is second-in-command. It is now 6:23 am. and Japan faces one day which they never have before.