Complete Monster/Bokurano


 * Masaru "Kodama" Kodaka, the second child to pilot Zearth in Bokurano (also from child-friendly mangaka Mohiro Kitoh), loves the rush of fighting the enemy in an urban district, gleefully justifies the reckless killing of bystanders by claiming that "it was their fate" and that a million deaths are outweighed by saving the whole world, and wants to destroy even more to provide business opportunities for his father, a Magnificent Bastard who is the only one he looks up to.
 * Then there's Dung Beetle in the anime, the 'cute mascot' who is utterly unsympathetic toward the doomed kids and even takes a perverse joy from seeing their misery - that's not to say he's a saint in the manga, but at least there, he eventually gets some Character Development and mellows out a bit.
 * In the manga, the most evil character has got to be Morihiro Hatagai. What he does to his student and lover Chizuru "Chizu" Honda is completely and utterly horrible, so it's no wonder the girl goes Yandere once he breaks her. He's considerably toned down in the anime, though, but still above Jerkass level; in the manga, he's so sick that, was trying to stab him after one talk.
 * And the worst part is  Crapsack World, indeed.