headcannon : THE FORBIDDEN ONE
〷 This is a HC post focused on the villainous persona Gundham set up for himself!
Gundham outwardly puts on a great spectacle of being this dark persona, and a villainous character in front of the others. From calling himself the Supreme Overlord of Ice, to controlling the dark arts, to being a vile offspring that shouldn't have been created. He sets up this evil character that gives him some grain of confidence in his existence, and he plays it out until the very end, which gives him satisfaction in his own execution.
The trigger for this persona, I would say, was the death of his mother. I like to HC that where he says he was born of an 'Angel' and a 'Demon', he refers to his mother as an angel, and his father as the demon. An illegitimate son that was born off a false union, which guessed at maybe a man cheated on his spouse with Gundham's mother, and he was then born. To which the father had nothing to do with them, and left his mother a single caretaker. Its implied he cared for her, and that she did her best to take care of him. Feeling guilt that he couldn't even afford a toy car as a child, and that he would eat her terrible, 'poisonous' food so that she wouldn't cry from doing her best. Gundham states that losing the one thing he loved was his fall into darkness, and I believe this implied when his mother passed.
Getting to this persona may have come from his love of the occult, and how in his mind, he viewed himself. Seeing himself as illegitimate, and unwanted by his own caretakers. A burden. He viewed himself negatively from the start, and turned that into an evil persona for himself.
I HC that his mother passed away by growing ill, and blamed himself for it since he always saw her pushing herself too far to take care and raise him. This also pushes his belief that he is poisoned, and that his poison can even inflict those he gets too close with, which caused her to get ill, in his belief. He did it to her, and now all he had left were his animal companions.
This villainous persona gave him confidence, as he broke out of his shell and was able to express himself in a self-deprecating kind of way, mixed with narcissism. He truly believes he is from the Underworld, a cursed being, and loathes getting close to anyone else in fear his curse will inflict itself upon them as well, and they too will pass from his life. Even during his execution, Gundham relieved his evil character, so that the others may see him defending his deed and become the bad guy, so they would feel less guilty of damning him to his punishment.