Ryou is a genius. In episode 36, his father mentions that his IQ was over 180 at age of 10. He is headstrong, stubborn, rude, sarcastic, and occasionally anti-social. He teases Ichigo Momomiya a lot, but he has saved her on many occasions when she has transformed into her cat form. Also, he encourages Retasu Midorikawa to be more confident.
Ryou has tan skin and blond hair. He is tall and has aqua blue eyes, and is 15-years-old. When he's a cat, his eyes remain the same colour. Ryou's Mew mark is on the side of his neck, but he hides it with the collars of his clothes.
Tokyo Mew Mew
When Ryou was 10, a Chimera Anima attacked his parents's mansion and killed them when he was out with Keiichiro. He tried to fight the Chimera Anima but Keiichiro held him back. He moved to America with Keiichiro and spent the rest of his childhood there, but then returned to Tokyo to perfect his father's work.
Tokyo Mew Mew a la Mode
After her first day of school, Berry Shirayuki almost falls down a set of stairs, but was saved by Ryou, who caught her. He then invites her to the Café Mew Mew and she accepts, then goes there to admire the treats that were being displayed.
Later, Ryou catches Berry by surprise and she falls into a pastry display. She runs away, and goes through a DNA infusion machine, which merges her DNA with that of two endangered animals: The Amami Black Rabbit and the Andes Mountain Cat. She passes out and when she wakes up, Ryou gives her a robot named R2003, which she nicknames Ucha.
The Mew Project
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.
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.
- Ichigo Momomiya: Ryou seems to have a crush on Ichigo, and has kissed her many times to change her back from a cat into a human, though he is rude and demanding to Ichigo. He often likes to tease her.
- Retasu Midorikawa: Retasu used Mew Aqua to transform herself into a half-porpoise and kissed Ryou, but her feelings were one-sided so they decided to be just friends.
- Tokyo Mew Mew English Manga (Kodansha) - Ryô Shirogane
- Tokyo Mew Mew English Manga (Chuang Yi) - Ryo Shirogane
- Mew Mew Power - Elliot Grant
- Vajzat Mjau - Mbrojtëset e Planetit (Albanian) - Alban Udhëheqës
- Mew Mew Amiche Vincenti (Italian) - Ryan Shirogane
- Dong Jing Mao Mao (Mandarin) - Leng BaiJin.
- Dung Ging Miu Miu (Cantonese) - Ling BaakGam
- Berry Berry Mew Mew (Korean) - Jae-hee Gang
- טוקיו מיו מיו/Tokyo Mew Mew (Hebrew) - Rayou Shirogane
- Mew Mew Power (Season 1 Portugal) - Elliot Grant
- Tokyo Mew Mew (Season 2 Portugal) - Ryan Shirogane
- Tokyo Mew Mew (Japanese) - Kouichi Touchika, Junko Minagawa(Age 10, Episode 36)
- Mew Mew Power (English) - Sean Schemmel
- Mew Mew Amiche Vincenti (Italian) - Davide Garbolino
- Dong Jing Mao Mao (Mandarin) - Jie LiuPeng
- Dung Ging Miu Miu (Cantonese) - Man NgBok
- Berry Berry Mew Mew (Korean) - Kim Il
- Vadmacska Kommandó (Hungarian) - Károly Moser
- Miau Miau Power (Latino Spanish) - Wolfang Galindo
- טוקיו מיו מיו/Tokyo Mew Mew (Hebrew) - Daniel Zilberstein (Season 1, Ep. 1-26) / Dor Sarugo (Season 2, Ep. 27-52)
- Mew Mew Power (French) - Christophe Hespel
- As Super Gatinhas (Brazilian Portuguese) - Thiago Longo
- Mew Mew Power (Season 1 Portugal) - ???
- Tokyo Mew Mew (Season 2 Portugal) - Quimbé
- โตเกียวเหมียวเหมียว/Tokyo Mew Mew (Thai) - ???
- Mew Mew Power (Danish) - Simon Stenspil
- Mew Mew Power (Dutch) - ???
- Družina Mjau - Mjau/Mjau - Mjau Tokio (Serbian) - Nebojša Milovanović
- Силата Миу Миу (Bulgarian) - ???
- Mew Mew Power (Greek) - Stamatis Gardelis
- The different meanings for Ryou's first and last names have a lot to do with wealth. "Ryou" can mean "angle", "edge", "corner", "power", "majesty", "dragon" and "spirit", and his last name, "Shiro" can mean "white", "gane", (money, or gold) and "platinum".