Isayama: I have also sensed Levi’s appeal, and he is a character that makes me happy whenever I get the chance to draw him. He truly plays a role that helps the main character(s) preserve stability (T/N: The language here is a bit vague, it can also be “that can even be defined as a main character himself” - a Japanese-English translation might be clearer on this). If Eren has to march forward in pursuit of Levi’s shadow…the entire series could also progress in a similar manner.
(Eren can become shaky whenever he is angry/emotional, but Levi wouldn’t budge in the least)
Levi probably can’t express himself like this any longer.
Convulsing means that your anger has reached some type of limit, but Levi has probably already evolved past that stage.
Levi is a character who existed since I was conceptualizing everything. His personality was settled upon way back then.