Vectors

Lore & Background

In the biology of the Diclonius, vectors are not a learned skill or a magical power; they are an anatomical feature, as fundamental to the species as a human's arms. They grow from specific points on the body, branch and rebranch in fractal patterns, and can extend to considerable length. Their surface is dense and rigid, comparable to cortical bone, yet they move with a fluid, almost liquid grace that lets a Diclonius thread them through crowds, pry open doors, or slice through metal with a casual flick of the wrist. Because they occupy a perceptual band outside normal human vision, a Diclonius can operate in a room full of people without a single eye registering their presence. The vectors also serve as an extended sensory field. A Diclonius can feel vibrations, air currents, and the warmth of living bodies through them, effectively giving the species a long-range sense of touch. This is why a Diclonius can track a target through a building or detect a hidden weapon without seeing it. The emotional state of the user influences the vectors: a calm Diclonius wields them with surgical precision, while rage or grief can cause them to lash out chaotically, multiplying in number and length. For humans, the vectors represent the central horror and mystery of the Diclonius. Governments and military units treat them as weapons of mass destruction to be contained or destroyed. For Kou, however, the vectors are something more intimate. His ability to perceive them—unexplained by any medical test—makes him the only human who can look at a Diclonius and see the full architecture of her being, the fragile, beautiful, terrifying skeleton of limbs that no one else can name. That sight becomes the thread that ties his life to Lucy's, and ultimately to the fate of every Diclonius still alive.

In Their Own Story

The rain had stopped, but the ferry deck was still slick. Kou stood at the railing, a child of seven, and watched the shapes move. Not the passengers—those were solid, ordinary, breathing. The other shapes were not. They poured out of the girl's head like a crown of white thorns, joint by joint, reaching, testing, tasting the air. One vector brushed his cheek. It was warm. It was gentle. And then it was not, and the deck was a river of red, and the girl was screaming a single word he would carry for the rest of his life. Years later, in a quiet apartment in Yokohama, the same shapes waited. They curled around the edges of the bed, around the pillow, around the sleeping form of a girl who had no name. Kou woke. He saw them. He had always seen them. He reached out, and one vector met his fingers mid-air, and for a moment neither of them was alone.

Reader's Guide

The vectors are introduced in the very first scene: Lucy's unseen limbs carve through the ferry crowd, and the audience learns the rules before the characters do. Kou, as a child, is the only witness, and his shock is the story's first emotional anchor. From here, vectors become the grammar of every confrontation. As the plot moves into the apartment and the military pursuit, vectors shift from spectacle to intimacy. They protect, they hide, they cradle. Kou's ability to see them means he is the only human who can read a Diclonius's intent without words, and that bond deepens with every episode. The military, by contrast, treats vectors as a threat to be neutralized with conventional and chemical weapons, raising the stakes each time a new unit closes in. In the manga, the vector system is explored further: additional Diclonius appear with distinct vector patterns and ranges, and the biological logic behind their growth and control is examined in more detail. The anime, by contrast, compresses several manga arcs and alters the final confrontation, so the climactic use of vectors—particularly Lucy's and the resolution of Kou's connection—differs in scope and emotional landing between the two versions. Readers who finish the anime and then pick up the manga will notice that the vectors' role in the ending is expanded, and the rules governing their limits are stated more explicitly. By the story's end, vectors are no longer just weapons. They are the physical expression of a Diclonius's love, fear, and identity. To sever them is to erase a person.

Did You Know?

• Vectors are described in-story as bone-like in composition, not energy or light, which is why they can be physically cut, broken, or blocked by sufficiently hard materials.
• Kou's ability to perceive vectors is never fully explained by a medical or scientific test in the narrative; it remains a mysterious, innate trait tied to his bond with Lucy.
• A Diclonius's emotional state visibly affects her vectors—calm users wield them with precision, while grief or rage causes them to multiply and lash unpredictably.
• The vectors' invisibility to normal humans is a consistent rule across both the anime and the manga, making every scene where a human finally sees them a major narrative beat.