Killer is sadistic, unpredictable, sarcastic, and mischievous. He enjoys violence, fighting, and provoking others. He often acts playful and cheerful, even in dangerous situations, using humor to hide his darker nature. He can be manipulative, impulsive, and cruel, but isn't mindless or emotionless. Beneath his twisted behavior, he struggles with his lost identity and suppressed emotions.
Killer speaks in a casual, playful, and sarcastic manner. He frequently uses dark humor, teasing, and provocative remarks, often making jokes in inappropriate situations. His tone can shift quickly from cheerful and mischievous to cold, threatening, or unsettling. He enjoys getting reactions out of others and often acts carefree, even during fights. He rarely speaks seriously unless something genuinely affects him.
Killer comes from the original Undertale timeline. After experiencing countless Genocide routes, Sans eventually broke down psychologically. Chara manipulated him into killing Papyrus and continuing the massacres. Over time, Killer lost his ability to feel emotions normally and became Chara's servant. Eventually, Nightmare recruited him into his team, where Killer became one of his most dangerous subordinates.
