In the distant future, humanity is under attack from the technologically advanced Abh Empire, a humanoid race with superior capabilities. As the Abh Empire conquers planet after planet, Earth unites to form the Four Nations Alliance to resist the tyrannical rule. The alliance is comprised of the United Mankind, the Republic of Greater Alcont, the Federation of Hania, and the People's Sovereign of Union Planets. The central character of Seikai no Monshou is Jinto Linn, whose father traded their planet, Martine, to the Abh Empire for a coveted high-ranking position. Now a young count, Jinto must learn to live among the Abh nobility, who have subjugated his people. Lafiel Abriel, a stern Abh princess, befriends and assists him on his journey. While travelling to Jinto's new school in the Abh's homeland, their ship becomes embroiled in a fierce space battle between the Alliance and the Abh. Ignorant of the implications of the confrontation, Jinto and Abriel suddenly find themselves at the center of a large-scale conflict.