Kaina lives in a small village, with elderly people who are worried about him, as there is no other village in the Vault of Heaven and they believe they are the last humans in the world.

Kaina's life was destined to change as soon as he met Riliha, which came as a surprise as the villagers in the Vault of the Sky didn't expect to see another human still alive.

In order to safely return Riliha 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 Riliha at the base.

The Valghians capture Riliha so they can strongarm the Atlandians into surrendering. The Atlandian soldiers engage in the battle to rescue Riliha and Kaina, but aren't successful. Riliha 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.

Kaina arrives in Valghia and notices that the fortress is something different than he imagined. The initial astonishment turns into desperation to get back what thieves have stolen right away.

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 Kaina?