Black Clover Fan Theory - Tumblr Posts
The Dark Disciples are not actually evil people by nature, but rather shaped like that because of their past experiences and the Devil possession (character analysis / theory)
Svenkin Gatard:

Sven in canon is a vain man that thinks Vanica loves him and seems to simp her very much. He also canonically loves bodybuilding. Given these two traits he has, most assume that he is an annoying and creepy simp madman. I will just get deeper to it and say that in his youth, he probably lacked much confidence and could never get a person to date or friends. That's my HC, but he has the body type where muscle and fat are easily gained (like mine lol, also obvious in canon about the muscles). So, he probably had super low self esteem because he could be chubby, and no one would like to date him. Could also be bullied because of his magic attribute, and / or his personality. At a point he discovered bodybuilding and regained his confidence, but also met Vanica and willingly set himself to undergo the devil possession and become a Dark Disciple, which changed him dramatically and made him the man he is in the Spade arc.
Sivoir Snyle:

Given his behaviour and interests in canon, I think Sivs suffer from OCD, and when he was younger, it had reached being unbearable. He also seems to be very weak as a character (afraid of getting hurt) and quite vain as well. He probably has spent most of his youth alone, because he could be repelling other people with his behaviour, or willingly not wanting Friends because of his suffering and fears. The idea of the devil protecting him in a way, since he'd be gifted with enhanced magic traits, eyes that could detect all kinds of danger for him, that sure convinced him to join the DDs, and of course the fact that one of the Zogratis - Vanica specifically - would chose him to serve her and him gaining more ranks in the military, given his said vanity. That way, he would finally get recognised and probably be relieved from his phobias at a point, but the Devil made him escape the limits of sanity and constantly get more hungry for recognition and safety.
Halbet Chevour:

Halbet is a naturally beautiful woman and is also pretty vain. She canonically only loves her beautiful self as it is stated in her profile, and she is also seen using a syringe on herself to enhance her powers, something we didn't see by the other DDs. Her magic is quite beautiful as well, unlike her comrades that use kinds of body horror Magic. So that means that the syringe obviously provided her with more beauty, and she probably believes that strongly. He past self might have received a lot of jealousy from other women and people in general, and probably has been bullied for her weird hair. That has probably shattered her self esteem and she could have desired ways to boost her natural beauty even more. That lead her to the Dark Disciples and Vanica, whom see seems to admire a lot like her comrades. The Devil provided her with more power to her stunning hair, and now she could revenge for the hate and bitterness she had gotten from people, and obviously feel much better for herself as well, but like everyone, that lead them to madness and mass egoism.
Hischer Ongg:

We don't know much about Hisch yet, aside the fact that he is a DD of Vanica's, loves cooking (WHOLESOME BOI, ILY- clears throat sorry for that) and he has a constant smile on his seemingly innocent face. He also seems more quiet that the rest of his comrades. My theory for him is that he can't escape his truly kind self but painfully tries to because he has gotten hurt many times because of it. He was so kind in his younger years that he was used constantly for it. He tried to make friends but ended up losing everyone and always giving without receiving. He was always that weird kid everyone acted hypocritically around him to earn his favour. One day he just decided to stop this and harden his heart. He joined the DDs with the hope of the Devil corrupting him and making him act tough and selfishly to save himself from getting hurt, but also lost his sanity, and his old self is in constant fight with the Devil powers inside of him now.
Robero Ringert:

This man really gets the hate from the fandom, and even though I understand that he acts all creepy, I can see deeper in that. He is observed to love getting stomped upon to the point of bleeding and lick people and things he likes. He really is insane, or rather his past according to my theory has led him there. Well, he's obviously a very big guy and his magic can be repelling for many. But he was born like that, and it's unfair he gets all the hate just bc of these features. His younger self has probably experienced mass bullying and rejection, to the point of not knowing how to act socially anymore and start enjoying every bit of attention he would get, even if it meant being hated on. His heart is just numb after all the times it has broken. And that lead to him joining the DDs for the sole purpose of getting that attention he was starved for, and losing his mind even more after getting possessed.
*inhales* That's exactly what I wrote on Discord as well, I hope you like it!