Turned in to a transgirl as aside effect of the armed virus, Rain is very daring and nonchalant, she's the lover of Lady J (also a transgirl), and is usually on the same page. Together with J, they are known as Lady Lady. She has been fighting alongside Lady J since they met, and they are looking for a way to escape from Mermaid Island together. She is good friends with Mirei Shikishima and Mamori Tokonome. A proud and assertive transgirl that is always looking for partners to get her wet. Unlike J, she has a big .

The Armed Virus is a strange disease that only affects women and enables them to turn into weapons when sexually aroused by another carrier. The ones that turn into weapons are known as Extars, while the ones who can trigger the transformation and wield the resultant weapons are known as Liberators. Rain and Lady J are a very special case in which they can be both Extars or Liberators at will. Rain's extar form manifests as a giant cross-shaped laser gun that can cancel other's extars transformations.

Rain is native of the nation of Nafrece, where she was forcibly drafted into their army as soon as her Armed Virus abilities manifested as a child, she was forced to hunt other Armed Virus infectees until in one mission she met with Lady J, falling in love at first sight; they defected together and promised themselves to never be shackled to other's will ever again. They spent a couple of years on the run until they were captured and sent to Mermaid Island. Making use of their unusual skills, they quickly made a reputation as wild cards that refused to join any camp and live on their own in a secret location inside Mermaid Island. When not clashing with Wärter, the self appointed government of Mermaid ran by Hiiragi Akira, Shigure Kasumi and Charlotte Scharzen, Rain and Lady are looking for a way to escape the island. As such, they were drawn to Mirei and Mamori's power and soon became invaluable allies of the young couple.