...
大雪海のカイナ
In another world, an ever-growing Sea of Snow has engulfed the planet surface. The people struggle to survive living around the routes of a massive Orbital Tree, whose branches spread into the Celestial Membrane high above the ground. Change comes to this dying world after Kaina, a boy from the Celestial Membrane, encounters a girl from the surface called Ririha.
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...
Kaina and the other villagers find out for the first time that there is life below the Canopy. Ririha, princess of Atland, explains that she came from the Snow Sea in search of "the sage," who may be able to help with their water shortage issue.
In order to safely return Ririha to her nation, Kaina goes with her to assist their climb down the spire tree, knowing he will not be able to return to his village again. Their travel goes smoothly, but the Valghians were waiting for Ririha at the base.
The Valghians capture Ririha so they can strongarm the Atlandians into surrendering. The Atlandian soldiers engage in the battle to rescue Ririha and Kaina, but aren't successful. Ririha manages to free Kaina while she remains in captivity.
After learning of the King of Atland's decision to not rescue Ririha and instead go to war with Valghia, it's up to Kaina and Yaona to go save Ririha. Without a means to travel the sea, they must figure out an alternative way to get there.
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.
After saving an innocent girl from being executed, Kaina, Ririha and Yaona are given a small boat to escape. Unfortunately, without any means to navigate the boat accurately, they are unsure if they're heading in the right direction.
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?
