Ryō Shirogane, born into affluence, exhibited extraordinary intellect with a verified IQ surpassing 180 by age ten. After a Chimera Anima attack orphaned him at ten by destroying his parents' mansion, he relocated to America under Keiichirō Akasaka's guardianship. He later returned to Japan to lead his father's Mew Project, which merges endangered animal DNA with humans to repel alien threats. Prior to human trials, he tested the procedure on himself, resulting in temporary transformation into a grey cat named Alto for ten-minute intervals; exceeding this duration risks permanent alteration. As Alto, identifiable by his green scarf, he frequently rescues Ichigo Momomiya by kissing her to revert her feline form. He conceals his neck's Mew mark with high-collared attire.

Sarcastic, stubborn, and blunt, Ryō often clashes with Ichigo yet actively supports the Mew Mews—bolstering Retasu Midorikawa's confidence and coordinating team activities. He develops unreciprocated romantic feelings for Ichigo after she pursues Masaya Aoyama, and in *Tokyo Mew Mew New*, declines Retasu’s confession to prioritize the Mew Project.

During *Tokyo Mew Mew à la Mode*, he recruits Berry Shirayuki as the sixth Mew Mew following her accidental fusion with two endangered species, equipping her with the robotic companion Ucha (R2003) and integrating her into the team amid Ichigo's absence. Post-series in the *Re-Turn* manga, he enlists reformed aliens Quiche, Pie, and Tart at Café Mew Mew to monitor residual Chimera Anima threats.

Multilingual and athletically agile, Ryō employs acrobatic leaps during missions. His scientific expertise and unwavering commitment to the Mew Project drive his relentless efforts to protect Earth, intermittently mentoring the Mew Mews while balancing leadership duties.