Complete Monster/Ichi the Killer


 * Jiro and Saburo from Ichi the Killer. Oh my god. It's hard to say what's the most terrifying the personalities of these twin brothers or their sibling rivalry which makes them bring out the worst in each other. These Creepy Twins practically oozed tension whenever they appeared, and their Uncanny Valley faces with features squashed together only added to their scariness. Their actions are so violent and insane that even their fellow Yakuza gangsters are shocked and disgusted. The twins cross the Moral Event Horizon over and over and over again; by the time Saburo rapes a girl to death by shoving a sword in her vagina, you barely feel anything.
 * Kakihara from the same is only slightly less twisted. An extreme sadomasochist, he hideously tortures and kills people at the drop of a hat, whether or not it's warranted. His actions are so extreme that everyone else in the Yakuza organization, and even most of the men under his control, are revolted by them.