What is the Work?
Rising of the Shield Hero is a light novel series (which recently recieved an anime adaptation) about a young man named Naofumi who is summoned to a parallel world along with four other young men, each of which are blessed with a powerful weapon to which they have an affinity and become the Cardinal Heroes. When our protagonist is given the possibility of choosing other party members, all of the other warriors choose the other heroes because of an existing stigma against the Shield Hero, with the exception of a young girl (secretly the kingdom's princess) named Malty (going under the alias of Myne).
Whilst the two initially seem to strike up a strong friendship, within a couple of days Malty steals all of Naofumi's equipment and falsely accuses him of raping her, leading to his complete rejection from society and forced exile from the kingdom he was meant to protect.
Who is the Villain?
Malty is one of the book series's main antagonists, and as stated it's her cruelty that sets the story's events in motion. Her father's tendency to spoil her as a child led to an enormous sense of entitlement and superiority, resulting in her behaving extremely cruelly towards her servants and especially her younger sister, resulting in her mother removing her from the position of Crown Princess at a young age.She is an ambitious, sadistic, and endlessly manipulative pathological liar manipulates her father based on his xenophobia and affections for her in order to try to be made crown princess, desiring to rule the kingdom of Melromarc for herself in part due to her own superiority complex.
What does she do?
Well, she falsely accuses the protagonist Naofumi of rape, spreads a large number of false stories and runours about him, attempts to murder her own little sister in cold blood to take the throne (and blame the crime on Naofumi), kidnaps and sells other members of the Spear Hero's party into prostitution/sex slavery if they get too close to him (so that she can be close to and manipulate him to her own ends), prevents people from joining Noafumi's party in order to enoy watching him suffer alone, attempts to remove Naofumi's party members after making further false accusations, colludes with the Three Heroes Church in order to kill all of the Cardinal Heroes, tricks the Spear Hero into thinking that Naofumi had murdered the other cardinal heroes in order to spark a fight to the death between the two for her own amusement, abuses her power to heavily tax poor villages, allows a dangerous magic duel to take place in her city, endangering the people she's meant to be prootecting, and continues to lie about her actions even in court.
Well, here's the thing: she does team up with the protagonists on several occasions when dealing with the existential threat of the Waves, but even then it's mainl for her own survival rather than anything else. For some reason the Spear Hero keeps her around in his party after her crimes are revealed, so he at least thinks that there might be something redeemable about her. There are also some possible moral agency issues with her due to her soul being a fragment of the evil goddess Medea Pideth Machina, so it coul be argued that she had no way to avoid becoming evil. However, she knew right and wrong from her mother's teachings, and stillactively chose to be sadistic and cruel to others because it was how she found enjoyment.
Here's another reason that she might be unstuck, and another reason why I'm not sure and wanted this to be discussed: The heinous standards of this work are insanely high, thanks in no small part to the absurdly evil villain Idol Rabier (who inexplicably doesn't have an article yet), a paedophilic mass-murdering xenophobe who massacres entire villages of demihumans and slowly tortures their children to death for his own sick pleasure.