Battle at Hohburg Fortress

The Battle at Hohburg Fortress took place mostly throughout the Replica and Never Ending Night arcs in the manga, and started with the appearance of the Shadow Man at Princess Ouka's birthday ball. The battle consisted of nine separate conflicts.

Verloren's defect
About a thousand years ago, the God of Death, Verloren, was found to have a "defect" in him that turned everyone and everything he came into contact with "black like mud". This defect would later also come to corrupt one of his fragments, Landkarte.

Frau's defeat and capture of Teito Klein
During the Hawkzile Race, Ayanami captured Teito. Frau tried to stop him, but Ayanami defeated him and an unconscious Frau fell down a chasm.

Relikt is devoured
Karu, the reincarnation of Ea at the time, contacted Lance, the vessel of Relikt, and told him about what Ayanami was doing to Teito. Karu then informed Lance that Teito was at the Oak House, and acting on this information, Lance went to the Oak House to try and contact Teito. However, unbeknownst to Lance, Ayanami had been waiting for a chance to devour him, and succeeded.

The Bishops' entry in to Hohburg
Frau, Castor and Labrador used Princess Ouka's masquerade birthday ball as an opportunity to disguise themselves and infiltrate Hohburg Fortress. Before long, fights broke out between the three Ghosts, Teito, Ouka, the Black Hawks, the Archangels, Nanase and Ouka's father, the Emperor.

Frau vs Teito
While still brainwashed, Teito attempted to stab Frau, but Verloren's Scythe protected him (Frau). Teito then regained his memories and emerged from the brainwashing, after which he set off to rescue Ouka, who was undergoing another experiment on the Eye of Raphael in the royal laboratory.

Castor vs Ayanami
Castor and Ayanami duelled. Ayanami eventually defeated Castor and attempted to devour him, but was unable to.

Labrador vs Hyuuga
Labrador tried to trick Hyuuga with an illusion, but Hyuuga was not deceived by it. Labrador offered Hyuuga a chance to protect and save Ayanami, giving Hyuuga a darkness-eating flower seed. Hyuuga accepted the seed despite Labrador's warning that he (Hyuuga) might be devoured. Hyuuga then headed to where Katsuragi and Konatsu were at, arriving in time to save Konatsu from Katsuragi.

Hyuuga vs Katsuragi
Hyuuga and Katsuragi duelled. Ayanami possessed Hyuuga and ordered Hyuuga not to fight Katsuragi. However, Hyuuga did not listen to Ayanami and eventually sacrificed himself to protect him, using the darkness-eating flower seed Labrador had given him.

Wolfram and Ouka vs Teito
While still brainwashed as a result of the Raphael Project, Ouka attempted to kill Teito on Emperor Wolfram's orders. However, Teito used the light of the Eye of Mikhail to help Ouka overcome the brainwashing.

Raphael vs Nanase
After emerging from the brainwashing, Raphael possessed Ouka and protected her from Doctor Nanase, who died almost instantly after Raphael stabbed him through the heart.

Karu vs Katsuragi
Karu and Katsuragi faced off inside the Book of Hades. Katsuragi eventually killed Karu, escaped the Book of Hades, and set off in pursuit of Teito.

Ayanami vs Ouka
Ayanami threw Ouka into a wall, and Ouka realised that her 'predecessor' had unsealed the Eye of Raphael. She then fell unconscious and Ayanami left her lying on the floor after defeating her.

Frau and Teito vs Katsuragi
After reuniting with Frau, Teito is attacked by Katsuragi, who has managed to catch up with him. Teito sees Katsuragi's 'heart', which has not become corrupted like the rest of him (Katsuragi), and grabs it. Frau says 'It's time for repentance', and as of Kapitel 92, the outcome of this battle has yet to be revealed.

in Kapitel 93, it is revealed that Katsuragi did not survive his battle against Frau and Teito. With the help of Teito and the goddess Eve, Katsuragi escaped the Ninth Layer of Hell and ascended to heaven, alongside his old friend Karu.

Aftermath
After the Battle at Hohburg Fortress, Verloren revives.