Tomoe Marguerite started out as a manipulative bully and Alpha Bitch who was in love with Shizuru, but after joining the Schwarz, she refused a Last-Second Chance to rejoin the Alliance and threatened to kill them all because she enjoyed making people suffer and the lives of everyone but Shizuru was meaningless to her. She later says she does so because she "always get[s] what [she] want[s]", pretty much cementing her "heartless bastard" status in the eyes of a lot of fans. Her Karma Houdini status doesn't help.
Her "Monster" status is cemented earlier than that, when it's learned that she attempted to have Arika raped so that Shizuru won't be as close to her, and to ultimately strip her of her Otome powers.
Nagi, the Big Bad of the setting, is a dictator who takes over Windbloom, releases forbidden technology, and starts a world war, supposedly to encourage evolution, but in the end, he reveals he just wanted to see if humanity would kill itself if given the chance. He is taken lightlyat times, especially before he puts his plans fully into action, but it is clear that he has no morals and everyone obeys him out of fear.
Manga
In the manga, Tomoe is Demoted to Extra and displays none of the repulsiveness of her anime counterpart. Her Complete Monster credentials are passed over to Big Bad Sergey Auguste Taiki (a far cry from his Punch Clock Villain counterpart Sergay Wang in the anime), who believes that the world is full of lies and needs to be destroyed for things to be put right once again. Not only is he abusive and cruel towards protagonist "Manshiro", and not only does he manipulate most of the cast, but he also frees the dark HiMEs and manipulates the Not Quite Dead real princess Mashiro in order to achieve control over Dark Mai and Fumi, using them as weapons to achieve his ambitions. Then, with Fumi under his control, he murders Mashiro when he didn't need her anymore and starts wreaking havoc on the world, while raving that the truth doesn't exist and that the "fake" world needs to disappear. He is only stopped by a Big Damn Heroes moment from Ensemble Darkhorse Erstin and a spectacular Combination Attack from the main Power Trio (Arika, Nina, and Ers) that takes out Fumi. As he lays dying, though, Sergay gets one last hurrah and manages to trick "Manshiro" into coming close, nearly killing him, stealing his Pure White Diamond and going One-Winged Angel to completely destroy the world. "Manshiro" turns out to have survived somehow, though, and with the help of all the Otome put together, he destroys Sergay after giving him an awesome "The Reason You Suck" Speech, pointing out how Sergay never loved anyone, not even himself. A pretty bad SOB, to be the counterpart of an overall decent person, huh?
