When the Armored Giant is finally released from Gowther's armor, it's revealed to be a former Holy Knight whose body has been horrifically mutated. It is can be best described as a fleshy creature with four demonic heads and hands whose fingers are actually complete human arms. When the first attempt to kill this thing fails, its arms rip apart to double their number and its heads merge into a single four faced single mouthed one. Smack in the middle of this all is the original host's head which looks almost lifeless as if the whole thing surrounding him is just one big uncontrolled tumor.
After getting hit by Gowther, Dreyfus wakes up to what appears to be a memory of him and Hendricksen when they were younger. Things however are not all what they seem. A hanged man can be prominently be seen. The town is filled with human faces situated on the walls and the ground. Characters start saying strange things such as children declaring that if there isn't gonna be a Holy War, they'd be the ones to start it. Copies of Hawk are seen littered throughout being mutilated and eaten. One of the foods Dreyfus is even served with is what looks like a human faced caterpillar. Then all of a sudden, Zaratras' corpse still in its Human Pincushion state confronts Dreyfus and begins to bleed all over Dreyfus from its eye sockets and mouth. All the while, Dreyfus repents that he didn't mean to kill his brother as he slowly transforms into a small groveling child. At the end, Gowther appears towering over the child Dreyfus and it's revealed that the Sin had basically Mind Raped the Great Holy Knight via his power over illusions.
In the Side Story 2 we found out that the reason Helbram hate human so much was that Helbram and his fairy friends met a group of humans who kidnap them and slowly tear out their wings for money as Helbram watch in tears as his friends died. This cause Helbram to grow a misanthropy for humans and end up transform his appearance to the person who killed them as a reminder of his hatred.
The Armored Giant mentioned above? All of the 2nd generation Holy Knights start transforming into similar horrors in chapter 85.