Lucia Nahashi is a strong, 15-year-old girl who lead the fights against Viruses alongside the other members of the Venus Vanguard, sworn to fight and kill all Viruses. During the day she runs a clothing and jewelry shop called Venus Vanguard. Some clients--those who come in with one of the fliers and happen to have the sight--can read the hidden message about Lucia's Virus hunting business and come to her for help.
Lucia appears strong, but inside she is still a scared and lonely little girl. She works hard to fight that part of herself though, and does a great job covering it up most of the time, rarely letting on that she is vulnerable except when she has been worn out by using her powers, or is seriously injured.
Lucia has long light blue hair that she wears in pigtails. Her right eye is blue and her left eye is yellow and holds a mysterious power, though is almost always covered with an eye patch. Use of her powers is taxing and wears her out, but can often be disastrous to her enemy in many ways.
After a girl named Sumire finds and returns her lost broach, she invites her to come work with her (of course this is after using the girl as bait to catch a virus, shooting her, and then finding out she can kill viruses after being shot by the anti-virus bullets), since she can see the viruses, and (now) has the power to help fight them.
In Chapter 18 we finally find out that Lucia is 15 years old.