Tsugumi is a mystery. At first glance, she's wary, cold-hearted, and rarely speaks at length. She seems to be hiding something from the others. She is also initially quite distrustful of the rest of the group.
It's revealed that Tsugumi is a carrier of the Cure Virus, a rare genetic virus that enhances the body, stops its aging after five years, and has great curing power, being able to heal severe injuries in minutes and rendering her immune to nearly all diseases. She was kept as a test subject by Leiblich for eight years until she eventually escaped. Due to the fact that having cells that never "age" makes mutations very dangerous, she is often wearing a giant lemur suit when out in the sun to protect her from UV radiations.(Source: Wikipedia)