Prologue

Almost 20 years into the past, Goki Fudo, Flash Knight Lord, trained his twin boys to succeed him as the next knight. Although Sigma was the more talented one, Goki chose Leo as he felt Sigma didn't have the heart of a protector. Unfortunately, that didn't sit well with Sigma and he forsaken his knighthood. Leo never wanted to succeed as Lord and both brothers decided to restart their careers as Makai Priests. As adults, both dreamed about a solution to solve the Horror threat; both created the Gōryū. It's an advanced magical machine that helps priests defeats Horrors. While Leo made a small combat drone, Sigma had visions to create the ultimate one: Magōryū Idea. The most powerful anti-horror magical tool to ever be designed, Sigma teamed up with Mio (a love interest to both brothers) to search for a means to power Idea. With the help of Mio, Sigma realized Idea's power core needs the remains of a powerful horror and human sacrifices to realize Idea. However, Sigma has killed innocents to experiment on and intend to use Gyanon's corpse to power Idea. Mio tried to stop Sigma, but it led to her death. Leo vowed to stop his brother's mad crusade, but he disappeared. Sigma would later harness Gyanon's energy, to give him great magical powers. Leo would eventually gain prominence with his gōryū and became a priest of the senate, where he was called "The Second Coming of Amon."

Story

After Chapter of The Black Wolf and Red Requiem, Kouga's deeds as Garo promoted him to become a Senatorial Knight. Answering directly from the Watch Dog Grace, he is partnered with Leo to handle unique and difficult missions. Before answering the Senate's call, Kouga defeated a Horror when a Red Masked priest appeared and magically cursed him with The Mark of Death. Despite his mark, he accepted his promotion and secretly investigated into the matter without informing anyone aside from Leo.

As Kouga carried out his missions, the level of difficulty increased as he gotten weaker from his mark. He later finds out that Rei and the rest of the Makai Knights have all been marked. As they investigated deeper into the mystery (in between sealing Horrors), the knights suspected a Makai Priest(s) as it's clear that the attack was carried out by a magician. Eventually, Rei and Kouga fought Red Mask and unmasked him, surprised to see the face of Leo. Although the order now knows the face of their target, nobody was able to find Leo.

The truth is revealed after Kouga chased Red Mask after he stole the access key to the Madō Train. After Garo survived battling through a massive Horror's Den, Garo still had to face Red Mask and his gōryū. It was when Kouga was at his weakest that Leo arrived, revealing he's Flash Knight Lord. Leo tried to talk to Sigma, but he escaped. At Kouga's home with Zero, Leo explained about his past and his twin brother's mad quest. Although the truth has been revealed, nobody could stop Sigma. He revealed himself through a magical message, giving the knights an ultimatum: they need to forfeit their armor if they want to live.

At the Senate hall, the knights gathered to talk. Some were willing to give up their armor while others felt it's a dishonor, causing internal conflict. Kouga's title as Garo settled the knights down and promised to find a solution. However, this meeting was a trap. Sigma wanted to lure all the knights into a single place and trapped them in an unbreakable barrier. Sigma accelerated the death mark to hasten their deaths. With limited options, Kouga called forth Gajari (a powerful deity that's part of the order) to help transport his body where Sigma is so he could end the madness. Sigma had stolen the train and intends to use the moon's power to increase his powers. Garo managed to slice off Sigma's cursed arm (that made the marks), cancelling everyone's mark and saving all the knights.

The train crashed during the battle and Sigma salvaged the remains of the train and captured Kouga to travel into the Makai Realm. Once they entered the makai world, Sigma transformed the remains of the train and used Kouga's body to form Idea. With the help of Baron, Zero, Lord, Rekka, Jabi, and Kaoru, they managed to free Kouga, but Idea remains active. Garo and the rest of the knights attempt to stop it, but it was too powerful as it can regenerate any destroyed parts. When they invaded the control room, Sigma boasted the might of his creation, but he spoke too soon as his malice awakened Gyanon. The horror absorbed Sigma and took control of Idea. The entire automaton is now the new body of Gyanon. The might of the entire order descended upon Gyanon as the knights fought against Sigma's automatons and the priests prevented Gyanon from entering the human realm. Leo eventually suggested for the priests to give up their brushes, to allow the knights to create a powerful spiritual blast to take down Gyanon. In a coordinated effort, all the knights fired upon Gyanon and Garo finished Gyanon for good.

Despite restoring balance to the world, Sigma is still at large. It was while Kaoru prepared a feast for Kouga that Sigma took her hostage and forced Kouga in a duel to the death. Sigma knows he's dying, but he still had enough energy left for one last fight. Sigma was defeated, but Kouga's home was destroyed. When Gajari helped Garo, he promised to fulfill a favor for Gajari if he helped him and it was time for Garo to honor that deal. With little time, Kouga bid Kaoru and his friends farewell and he entered the Promised Land in search of a part of Gajari's body. Kouga's journey continues in Demon Dragon of the Blue Cries.