One night, the magical knight Ryuga Dogai who holds the title of "Golden Knight Garo," annihilates the horror Shauras. Then the magician Koyori appears. She has asked Ryuga for help in order to prevent the opening of the Gate of Destruction, the oldest gate where Horrors first appeared in the human world. Guided by Koyori, Ryuga visits Claire City, the city where the Gate of Ruin is hidden, and senses an evil spirit lurking in the bustling crowds...

The true identity of the Hagane, that bisected the Horror Regrege, was the Makai Knight Souma Shirahane. "This is my city", Souma says, checking Ryuga Dougai and leaving. Then, Mutsugi, a Makai Priestess, appears. She apologizes for Souma's rudeness and tells Ryuga of her orders to protect Creacity, which is in danger. At the same time, Igusa, Ron, and Obi, the Three Swordsmen of Agora whom Mutsugi had summoned, arrived in the city.

With the influence of the Gate of Destruction growing stronger by the day, Ron and Obi are hard at work training in preparation for the next crisis. Souma Shirahane, on the other hand, is alone in his frustration after witnessing the "Flash Sword" unleashed by Ryuga Dougai on a Horror. However, the situation is critical. Igusu asks Souma to protect Creacity with Ron, but Souma stubbornly refuses. Instead, Souma offers Igusu a proposal.

Godou Shirahane is involved in the anomaly of the Gate of Destruction.... Souma Shirahane drew his sword in anger at Igusu's statement. As his actions cause a stir, Souma admits his own faults as a Makai Knight and entrusts his Makai Sword to Mutsugi. Mutsugi, troubled, calls up Ryuga Dougai and confides in him about Souma's trauma. Meanwhile, new disturbing signs begin to emerge in Creacity...

An office building that has turned into a hive of countless Horrors as employees are possessed one by one. Ryuga Dougai, Koyori, Mutsugi, and the Three Swordsmen of Agora gather to address the unusual situation. Do not let the Horrors get out. It was Ryuga who stopped Mutsugi, who was about to place a ward on the building under the direction of Igusu. "We can't leave him out of the loop right now. This city needs Souma!" What decision does Souma Shirahane, who is struggling alone, make?

The "Night of Dawn", which is said to open the way to the "Sekigan Forest" once every three years, finally arrives. Ryūga Dōgai and Souma Shirahane enter the forest and encounter the spirit Rauru. Rauru offers one condition in exchange for the location of the "Stone of Eternal Darkness", the key to the Labyrinth of Arvis. Meanwhile, Creacity is a glittering city at night. There, Naomi, a employee at Crea Hall, looked at the brilliant dancers with envy.

Naomi, now a horror, devours Mari and attacks the fleeing Crea Hall audience. Koyori and Mutsugi rushed to the scene. Mutsugi invokes the gale and rushing winds of the Makai Priests and confronts Naomi's horror form Gaira. However, she finds herself in a predicament before Gaira's overwhelming power! Ryuga Dougai, Souma Shirahane, and the Three Swordsmen of Agora rush forward. How will the fierce battle unfold?

While being trifled by the intricate and bizarre mechanisms of the Labyrinth Arivis, Souma Shirohane sees the former image of his father, Godou Shirohane, in Ryuga Dougai, who cut down the horror Gaira. As Souma begins to realize what he lacks as a Makai Knight, Ryuga strengthens his resolve to convey Godou's words. The encounter between Ryuga Dougai the Golden Knight Garo and Godou Shirahane the Light Slash Knight Zango is revealed at last. And what Godou says about his feelings on his son Souma...!

Souma Shirahane and Mutsugi finally reach the Gate of Destruction. There, they saw the changed form of Godou Shirahane, the Light Slash Knight Zango who had hardened into a Lost Soul Beast form and was holding the Gate of Destruction in his arms. Mutsugi's expression turns cold in front of the shocked Souma... Meanwhile, Ryuga Dougai and Koyori, who have been transported to another space, are suspicious for Mutsugi's actions in the labyrinth Arivis. What is Mutsugi's true intention?

Mutsugi plans to open the Gate of Destruction and drive out humans with Inga. Souma Shirahane, who has been engulfed in his soul's darkness by Mutsugi's trickery, loses his sanity and thrusts his sword into the Lost Soul Beast form of Godou Shirahane’s Zango armor, which is the key to sealing the gate! Ryuga Dougai crosses swords in order to stop Souma from going out of control. On the other hand, Koyori stands up to Mutsugi even though she is conflicted. However, the seal of the Lost Soul Beast Zango is broken with each passing moment...!

The Gate of Destruction, which has regained its original form, causes a "forbidden fruit" which bestowed omniscience and omnipotence before Mutsugi's eyes. She promptly consumed the "fruit", attaining power boost she sought yet corrupted her at the same time. Ryūga Dōgai, Souma Shirahane, and Koyori stand against Mutsugi, who is trying to use a technique to purge humanity of their Inga. What is Inga? What is a human? The battle for the mission of the protector begins.

Mutsugi has been assimilated by the Seducer who aimed to plunge the human realm into chaos once more, becoming a Horror. Channeling her Inga, she altered Gate of Destruction into a more horrifying form. Golden Knight Garo and title-less knight Hagane, finally stand together to face a hopeless threat that will shake the world. Flash Sword Dance and Dark Flash Sword Dance — protectors, pass on the feelings you bet on Hagane to the future!