This person hasn't been mentioned yet, but I'm going to put it in a spoiler because the main characters begin the drama as a couple and then become exes (highlight the white text bellow to read):
Sousuke from Last Friends. He starts out as this well dressed, cute, considerate boyfriend. Then he begins to seriously abuse, stalk and restrict the activities of his girlfriend. When she tries to leave him, his activities escalated, and he brutally attacks the people who try to help her. He is truly the ex from hell. It's kind alike an extended, J-Drama version of that movie Fear with Mark Wahlberg and Reese Witherspoon.
