A young girl named Rin lives with her younger brother Al, older sister Mel and grandfather Talgia Hawkray in the faraway Dandera Village deep within a forest. Rin is devoted to go to the Capital and sing in the Court Orchestra, while Al is determined to show off his prototype inventions. However, Talgia refuses and even forbids Rin from singing. Rin and Al are given the opportunity to sneak out by venturing into the forest to pick berries, whereupon they stumble upon an injured knight from the Capital, later recognized as Henry Leobolt. Although Al wants to return to get medicine, Rin decides to treat Henry with the Song of Healing. After Henry formally introduces himself and tries to honor their wish of going to the Capital, ice mysteriously begins to spread throughout the forest, separating Rin and Al from Henry.

Henry returns to the Capital, only to be told that a war is upon the country in its competition for the power of their songstress, later recognized as Finis, whose songs can rejuvenate and heal soldiers. Henry refuses to see Finis as a tool to be used in war. Finis, a beautiful but clumsy woman, is forbidden to leave the palace tower, according to her maid Corte. The ruthless prince Rudo Bernstein IV intends to marry Finis and keep her bound to the castle. While Finis enjoys fresh air in the garden on a rare occasion with her attendants, she gets lost and almost killed by an assassin. Henry arrives to save her and earns the title of being her bodyguard.

Henry fights in the front lines alongside comrades Berrow and Snore. Finis later arrives on the front lines and put her life in danger to use her Song of Healing in order to revive the soldiers. Henry then hears word that Finis plans to use the destructive Weapon of Song against the enemy.

Corte realizes that a frail Finis is using her powers for war to protect Henry. Being told that Rudo would execute Henry if Finis did not use her powers against the enemy, Corte runs into the forest to gather herbs. When a knight tells Corte that Finis has gone to the watering hole, Corte instinctively runs back into the forest.

Henry reunites with Finis, Berrow and Snore in the forest. Although Corte is relieved to find them, Rudo arrives to take Finis to the Montvale Fortress, but Henry proposes that it can be captured without the use of Finis. Henry, Berrow and Snore ultimately conquers the Montvale Fortress. Meanwhile, Rin, Al, Pony, Monica and Allu find a cottage owned by Doctor Weissen, who has all sorts of contraptions.

While the front line knights celebrate with a banquet in honor of their victory at their army camp, Corte sternly warns Finis and Henry to run away.

In an alternate timeline, astronomer Henry predicts that the Moon has changed its orbit and will collide into Earth in about 60,000 years. When Henry and Finis meet, she tells him that she is a songstress who was blessed with the power to make miracles, until she used that power to kill her dearly beloved. According to her, life is an endless yet hopeless cycle between past and future

Finis, now in cloaked attire, is told by Bazra that her power of songs will achieve world domination, but she states that their prior agreement was for her to sing her Song of Mortality during the Starsong Festival. Rin, Pony, Monica and Allu realize that Finis has only been seen by a few knights of the Capital Army.

Rin was taken in by Talgia and Mel as a baby. Talgia was against Bazra's views of using Finis's power of songs as a tool of war. While dueling, Bazra used a fire echo device to disable Talgia's right arm from wielding his sword. After Talgia later held Rin by his left arm, Rin sang the Song of Healing to treat his right arm, as he vowed to always protect her.

Al reveals that his jet pack is powered by wind echo devices, but the weight of Rin causes both of them to fall. While Rin, Al, Pony, Monica, Allu, Henry, Berrow and Snore camp out, they spot an airship, which they assume that Bazra is heading to the Capital.

Finis and the Court Orchestra perform the Song of Mortality, forcing the Moon to start falling towards Earth. Henry, Berrow and Snore fight against Bazra, who is equipped with the new Symphony Killer.