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Jinto and Lafiel were riding on a light-armed transport ship "Bokbrusue" and navigating at the planar space of the Hyde System. This was for Jinto to govern the Hyde System, which returned to Empirial rule after the Union retreated, officially as an Earl. However, the government of Martin, Jinto`s motherland, resisted obstinately against the Empirial rule. On the other side, "Daiichi Jyuurin Sentai" (the First Devastation Fleet), formed with the new ship type "Attack Vessel", travelled to the Hyde System for drilling practices, but...

Due to a lack of ambassadors for the recently-conquered worlds the rapidly advancing fleet of the Bebaus brothers leave behind, Lafiel is appointed Territorial Ambassador of the planet Lobnas II. Upon arriving to the planet Jinto and Lafiel discover that the planet was used by the United Mankind as a prison planet and now has a million prisoners on the only inhabited island. The prisoners are parted in three blocks. The western where women are housed, the eastern belongs to the men and the central is mixed under the restriction that all prisoners living there are sterilized. The women in the western sector want to emigrate from the planet of fear for the men and when they do the men in the east rebel, overthrowing the guards and capturing Jinto to try to stop the emigration of the women. At the same time an enemy fleet heads toward the system forcing Lafiel to abandon Jinto.

Three years after their adventure, Lafiel becomes captain on the brand new assault ship Basroil and Jinto finishes his training to become a supply officer and joins Lafiels crew. They set out to join a large fleet with the mission of defending the strategically important Laptic Gate from a force 15 times larger than their own. And to bring even more worries, their new fleet commander is from the Bebous family, a family notorious for their "Spectacular Insanity".

In the distant future, humanity is under attack by the Abh Empire, a race of advanced humanoid beings possessing vastly superior technology. As countless worlds fall to the Abh, mankind establishes the Four Nations Alliance—a resistance faction made up of the United Mankind, the Republic of Greater Alcont, the Federation of Hania, and the People's Sovereign of Union Planets. Seikai no Monshou tells the story of Jinto Linn. When he was young, his father—the president of Martine—sold their world in exchange for a high position in the empire. Now a young count, Jinto must learn the ways of Abh nobility and live among those who subjugated his people. Helping him is Lafiel Abriel, an austere Abh princess whom Jinto quickly befriends. While traveling to Jinto's new school in the Abh homeland, their ship is caught in a violent space battle between the fleets of the Alliance and the Abh. Jinto and Abriel are thrust into the conflict, unaware that this skirmish marks the beginning of a full-scale war between the Abh Empire and mankind.

This is the story about how Dubus, Lafiel's father, and Plakia after an adventure on a mysterious, abandoned spaceship decided to have a daughter together and why Dubus gave her the name Lafiel.