Killua has spiky silver hair, very pale skin, and blue eyes. His eyes change shape depending on the mood that he's in, narrowing and sharpening when he goes into assassination mode. Killua is fairly lean at the start of the series, due to constant physical conditioning and torture training he received when he was young. He is also one of the quickest-thinking characters. However, his ruthlessness and aptitude in killing show the other side of him—deadly, violent, and bloodthirsty.