A phenomenon called the Snow Sea engulfed the surface world, and only a handful of people now reside high above the Snow Sea. When Kaina, one of the members of the last remaining village, goes on a hunt, he finds something entirely unexpected...

Once the Valghian admiral receives Atland's message that they will not surrender, he decides to leave Ririha outside to freeze to death. Luckily, Kaina and Yaona come to her rescue, but now they must figure out a way to escape and return to Atland.

Opting to stay hidden inside a box within the ship, Kaina, Ririha and Yaona find themselves offloaded to the mobile fortress of Valghia. Now, they must somehow come up with a way to return to Atland, but Valghians are hot on their tails.

Just before the start of the war between Atland and Valghia, Kaina and his friends race to get proof of a great tree that can save everyone, including their enemies.

Valghia have a fearsome weapon, a relic from the Age of the Sage, which they have activated. How will Atland be able to fight back, now cornered?

Drunk on power, the Admiral continues to operate the Builder and is determined to kill the King. Ririha tries to save her father, which results in making herself the Admiral's target. Will Kaina make it in time to save Ririha?