Sumire is a young middle school girl and the newest member of the Venus Vanguard, despite being terribly scared of Viruses. While initially she cannot be of much help to Lucia, they eventually find out that whenever her body reacts to the special chemical used to defeat Viruses (the so called Vaccine), she transforms into a "Berserker Mode", or a living Anti-Virus. With this strange ability, she becomes stronger and violent, and is capable of defeating Viruses with her bare hands, but when under the influence of this power, she cannot discern friend from foe, although over the course of the series she learns how to control her powers.