Since I'm aiming the title sequence for western audiences, and given Parasyte's got a humourous tone whilst still being dark and gruesome, I figured I'd take inspiration from Invader Zim, a rather depraved show, especially for a target demographic of kids. It's about an alien called Zim who gets sent to Earth from a faraway planet and tries to invade it whilst posing a school boy to avoid suspicion. Certainly one of the darker kid's shows , and the art style very much adds to that.
As you can see, the characters are all shaped very strangely and have very sharp and exaggerated outlines. Their eyes vary in size, but are generally known for being rather huge and disproportionate. The imagery, overall, is just really grim and surreal, so it suits the dark and twisted tone of the show.