Ryou Shirogane is a 16 year old wealthy high school student, the head of the Mew Project, and the owner of Cafe Mew Mew. Ryou is said to be a genius in the manga and the anime say that his IQ exceeds 180. After his parents' death when he was ten, he moved to Japan to continue his father's work with his father's assistant Keiichiro. After he finished developing the technique for injecting genes into the future Mew Mews, he first tested it on himself to ensure that the subjects would not be harmed.
As he was not a compatible host, it only gave him the ability to change into a cat at will for up to ten minutes at a time. Ryou also built Mew Ichigo's, and later Mew Berry's, respective robot assistants, R2000 and R3000. Ryou tends to talk to the girls in an abrupt manner, but displays a strong sense of personal responsibility, particularly with regards to the Mew Mews. He helps Ichigo several times, in his cat form, "Alto", including by kissing her to help her change back human.