Ryou comes from a wealthy family and has been stated to have an IQ surpassing 180, making him a natural genius, especially when it comes to genetics. It has also been rumored that he graduated from an American University. Because of this, and events in his past, he has a removed, sarcastic, and rude nature towards most of the cast, apart for his childhood friend, Akasaka-san. Despite this, he seems to be a kind person underneath, something that Ichigo catches on to later in the series, probably most obvious when he is trying to encourage Lettuce who has little self-confidence. He seems to have a romantic interest in the main character, Ichigo, but, these feelings are not returned. Ryou is headstrong and serious, but has moments where he will behave immaturely, such as his arguing with and teasing Ichigo.

Spoiler

Ryou is dedicated to the Mew Project. When Dr. Shirogane's (Ryou's father) project was ready, Ryou was unsure that it would be safe, so he tested it on himself. He didn't have the right genes, so he didn't turn into a proper Mew Mew, but does have the ability to change into a cat for ten minutes. If he stays a cat for longer than that, he is permanently stuck in cat form.

Spoiler

When he is a gray cat, he goes by the name Alto. He wears a green scarf around his neck. Alto was introduced in episode 28. Alto saved Ichigo's life many times and has kissed her in order to return her back into human form. Ryou is the one who gave the girls their Mew Pendants so that they could transform. He was also the one who (with Keiichiro) chose which people would get the Red Data Animal DNA implanted in them.

(Source: Tokyo Mew Mew Project)