The yearly familiar exhibition is literally a day away and Louise is feeling rather depressed about it. Not only does Saito have nothing impressive to show off, but this year the Princess is watching as well, making it even more important. As night approaches, desperation sets in as Saito is unable to produce an act worthy of praise. A sudden mystery visitor turns out to be Princess Henrietta herself and her relationship with Louise is explained. The next day, Saito attempts a presentation only to be dragged off early by Louise. Walking away from the stage, they witness a robbery in progress by Fouquet and her earthen golem. Failing to stop her, Fouquet is able to run off with the fabled Staff of Destruction.

With the arrival of Wardes and Louise alone, they meet up with Prince Wales in a seemingly deserted church. After finishing up business, Wardes suggests to Louise that they should just get married right then. Confused and repulsed by the idea, Louise tries to refuse his offer, but one of Wardes' allies comes out with a mind-control ring, forcing her into agreeing. With the Prince as the minister, the marriage proceeds and is nearly completed until Saito bursts into the church. Snapping Louise out of her trance, Saito rushes to rescue her. In response, Wardes kills Prince Wales, revealing that he is in fact involved with the rebels fighting the government Albion called Reconquista.

Louise tries to prevent Saito from looking at other girls, but her plan fails. The newly crowned Queen Henrietta assigns the code name 'Zero' to Louise for a mission. When they get home Louise insists she tell him about the misunderstanding that Agnes said. When he tried to explain she beat him until morning causing bruises all over his body. The next morning, Saito and Louise are informed that Henrietta has been kidnapped.

Saito and Louise are ordered to be at Scarron's inn to receive further instructions. They take their previous positions and costumes back, and are surprised by Gulio's appearance. Saito runs into Henrietta who asks him to protect her as she poses as a commoner in order to lure out one of her enemies. Saito and Henrietta evade detection from the soldiers searching for the Queen by behaving like sweethearts, while Louise learns of the details of the Queen's mission from Agnes. In a theater in town, while Scarron and his girls are in the middle of performing a play, Henrietta confronts her enemy.

Are Louise and Saito being sent on a suicide mission? Before they even consider their safety, the couple has one last thing to accomplish and Louise wants to make a covenant.

Louise has a nightmare where she loses the ability to cast magic. Awakened, she goes into the forest to attempt to cast explosion. Saito finds Tabitha reading a book, and she began to teach him the words, but Louise interrupts, telling Saito that she can no longer use magic. Tabitha saids that she will protect Saito since Louise is unable to do so. In Tristan, Henrietta dispatches the Ostland and Colbert to rendezvous with Saito, carrying a type of cannon (which seems to be a German Flak88 from WW2), and Agnes offers the assistance of the Musketeer Force. Silently, Colbert hopes the weapon will not be needed. Saito, under Tabitha's guidance, learns to read quickly, while Louise broods over her inability to cast magic. Overhearing Tabitha telling Saito that under the influence of Gandalfr, the heart will experience changes, Louise wonders if Saito loves her because of Gandalfr's influence. Just before crossing the border, a Square-class golem, with Sheffield on its shoulder, lands in front of the carriage and blocking off the route into Tristan. Slyphid and Tabitha take to the air, in order to lead Sheffield away. Guiche, Kirche and Tabitha's attacks prove ineffective against the golem, which is protected by Counter, but they manage to halt the golem's advance with their spells. Saito realises her objective is Louise, and tells her to stay back, but she jumps out of the carriage as Malicorn pulls it back. She is grabbed by the golem, who began to crush her unless she uses her magic. Saito's attacks are easily stopped by Counter, and Louise decides to sacrifice herself for her friends. Saito leaps to attack the golem again, and this time, his attack damages the golem, which releases Louise, and Slyphid saves them in time. Colbert has unloaded the cannon, which Saito examines using his Gandalfr powers, and quickly fires at the golem, but the round is stopped by Counter. Colbert, Kirche and Maricom unleash their most powerful spells, and manage to stop it's advance. Derflinger tells Saito that Dispell needs to be cast on the shells, and Louise refuses, saying she can't do it. Tabitha then kisses Saito, eliciting feelings of intense jealousy in Louise, causing her void powers to be activated again. Louise casts Dispel on the ammunition, which successfully pierces the Counter and destroys the golem. On the Ostland, Louise awakens to see Saito, and asks him if she's okay like this. Saito hugs her, and again declares his love for her, saying he does not love her just because he is Gandalfr. Then Louise kisses Saito while claiming that she has to because he's her familiar. Back in Tristan, Louise kneels before the queen, awaiting punishment for defying her. Henrietta punishes her by awarding her the royal mantle, declaring that Louise is now her sister and second successor to the throne, as well as returning Saito his Chevalier cloak. She then welcomes Tabitha as Princess Charlotte back to Tristan. The ending credits also show Maricom and Guiche wearing their mantles with their school uniforms, signifying that Henrietta has reinstated their noble status. When Louise tries to explode Saito when she sees Tabitha holding onto Saito, Sylphid grabs Saito and escapes with Tabitha.

After the discovery of a hot spring on their land, Saito decides it is the perfect time to have a hot springs party. Though he invited everyone, an unforeseen guest appears and shocks the crowd.