The class of 3-Plum heaves a sigh of relief after Horizon Ariadust, now the automaton P-01s, and Toori Aoi finally reunite for the first time. Afterwards, Toori hands over the certificate that officially enrolls P-01s into Musashi Ariadust Academy. P-01s quickly accepts the invitation into the Far East's primary academy, and Masazumi echoes the declaration of P-01s as a student, now under the jurisdiction of Musashi Ariadust Academy's Student Council and Supreme Federation.
Innocentius watches in disbelief as the forces of Musashi are ordered to retreat by Naomasa, who boards one of the derrick ships of the Musashi. He decides to escape while the troops of Musashi fall back, but Toori decides to pursue him. Fortunately, P-01s urges him to leave the Steisos Porneia behind for the meantime.
Masazumi, onboard the derrick ship of the Musashi , tells the two to hurry and get aboard. However, Innocentius, pointing out that P-01s' enrolment is unofficial until she boards the Musashi, fires upon the derrick ship, forcing it to perform evasive actions. Toori signals to the ship to give him one more chance to board the ship, and Nate steps up for the job; with Nenji's shape-shifting ability and the Argentées Chaînes, she reels in Toori and P-01s with little time for K.P.A. Italia to respond.
Soon, the Eikoumaru takes off without the Pope-President and takes pursuit of the derrick ship, vowing to pursue the fleeing ship at all costs. The Eikoumaru manages to close in on the derrick ship and sees the Musashi taking off as well, but its pursuit was drastically slowed down when Futayo Honda, aboard the Mikawa Security Corps' ship, uses the Tonbokiri to inflict damage to the Eikoumaru. The ship then tries to avoid the Eikoumaru from colliding onto the derrick ship by tugging them using numerous harpoons, but the Eikoumaru manages to shake them off.
In another attempt to take down the fleeing troops of Musashi, the Eikoumaru is ordered to ram into the Musashi by using one of their ether cannons. Futayo decides to use the Tonbokiri for one more time, but is later warned against using it for the meantime. Toussaint, meanwhile, decides to utilize P-01s and allow her to use the Lype Katathlipse to take down the Eikoumaru.
With the Mikawa Security Corps' ship as the "platform", the derrick ship hoists P-01s and Toori and P-01s prepares to fire using the Lype Katathlipse's Normal Drive. The Eikoumaru and the Lype Katathlipse meet, and within seconds, the ether cannon is pushing back the Mortal Sin Armament. And to make things worse, the ether needed to sustain the attack is now being depleted.
For the first time, Horizon feels sad... after remembering the memories of April 20, 1648, the last time she had seen her father and the destruction of Mikawa, she feels her first emotion: Sadness.
During this period, the Lype Katathlipse's Hyper Drive is awaiting activation, and with Toori providing the ether needed to power the Lype Katathlipse, the Mortal Sin Armament fires onto the Eikoumaru.
As the Eikoumaru, now ripped asunder by the Lype Katathlipse, falls to the ground, P-01s sings the "Song of Passage".
P-01s, now overwhelmed by experiencing sadness for the first time, drops the Lype Katathlipse and asks Toori if emotions do feel painful. Toori assures her that these things are only temporary as they will have lots of fun after they have gotten all of the Mortal Sin Armaments, and requests her to endure until that moment comes.
Meanwhile, the defeated gather themselves up. As Muneshige Tachibana is carried back to Tres España's Inquisition Warship, Gin tells him that things have only just begun. On K.P.A. Italia's side, Pope-President Innocentius bitterly stares at the Musashi as it leaves behind Mikawa.
Later that night, as Mitsuki Sanyou heads back to her house, Makiko Oriotorai and President Tadatsugu Sakai talk under the foliage of trees in the Musashi. Sakai tells her that there's a festival in the Musashino commemorating Class 3-Plum's success in rescuing P-01s. He then expresses his interest in Makiko work record, which Makiko humbly attributes to her students. Makiko soon tells some info about the Aoi family, vital information that is surprising to be heard from someone like her.
Soon, their comfortable talk is interrupted by a strange seal left in the tiled floor in front of them: a Nikyou Crest, a sign of a spiriting away.
Then, things take a more serious turn when they see the ironclad ship of one of the P.A. ODA's Five Great Peaks — a certain Katsuie Shibata. Sakai explains that they are not here to be hostile, but only to show their might, which can at least detect the Musashi even under stealth mode. Soon, six figures are seen aboard the ironclad ship, which Sakai calls the "Six Demon Army".
As the P.A. ODA ship leaves the Musashi, Makiko sees strange writing on the Nikyou Crest.
"Please kill me... all."
In the Musashino, Nate accompanies Masazumi Honda as the latter wears female clothes for the first time. Nate asks about her plans, and while Masazumi explains her plans for Musashi's next destination, Nate points out that she is pertaining to her personal plans. Masazumi tells Nate that she is planning to go to England and gather connections as the Musashi undergo repairs in IZUMO.
Soon, they hear a ruckus just ahead of them, and they discover that the rest of the class is there.
Tenzou, Ulquiaga and Ohiroshiki decide on their respective plans for the next eroge they will play; Kenji is busy having a good time with Nenji, Hassan is serving wine curry for everyone; Adele, Suzu and Persona quietly help themselves; Margot and Malga snuggle while already asleep; Toussaint fixes some paperwork; Futayo is knocked out from drinking too much sake. In all of this festivity, Shirojiro and Heidi are contemplating at the expenses involved in the party.
Masazumi proceeds to scold everyone on what they are doing, but Kimi tells her that they are celebrating. As Kimi takes interest in Masazumi's new clothes, she mentions that the Blue Thunder's shopkeeper is actually her mother, and Masazumi laments at realizing it too late.
She then wonders where Toori and P-01s are, and she finds them inside Blue Thunder, soundly asleep. As Kimi and Nate accompany Masazumi in watching the two sleep, P-01s sings the "Song of Passage" one more time. Masazumi, after the song ends, realizes that tomorrow will be another beginning for everyone.
Kimi then remembers that Horizon requests breakfast from Kimi. Masazumi wonders if they would enjoy it together, and Kimi only worries about how the two would react if the breakfast tastes bad.
And the taste eventually turned out... nostalgic... indeed.
Three weeks following this night, May 14, 1648, Muneshige Tachibana is lifted of his position as Tres España's First Special Agent. Gin is alarmed by this, but decides to fight in the battlefield in his behalf to prove that dismissing Muneshige — who is regarded as a stronger fighter than her — might have been a mistake.
Soon, fellow students of Alcalá de Henares report that the Musashi has been spotted on the west.
Just as reported, the Musashi is seen on the domain of Tres España, Shimonoseki, and the Musashi is immediately confronted by two Kraken-class and six Wyvern-class ships, including the Kraken-class San Lorenzo. Toussaint estimates that the forces of Tres España is there only to defend their skies, and striking first is not an option.
With the Musashi under threat of enemy fire, Class 3-Plum is engaged once again.
They face new foes, including the pitching specialists Pedro and Flores Valdés with their specialty ability "El fuego de St. Elmo", the batting specialist Takakane Hironaka, and the God of War controller Era Fusahide, led by Juana, one of the highest-ranking members of Tres España.
To avoid further damage, the Musashi enters gravitational navigation mode in an attempt to escape Tres España's airspace at the shortest possible time.
Meanwhile, where are Masazumi, Toori and Horizon in all of this?
Stay tuned, for Summer 2012 will be the start of Kyoukai Senjou no Horizon Season 2!