The Blue Knight is an enigmatic male character who makes his debut at the end of the fourth volume of the manga. During a confrontation with Kish at an aquarium, Ichigo finds herself on the brink of defeat when the Blue Knight suddenly appears and saves her. He tells Ichigo that he "belongs to her" and was "born to protect her."
Throughout the series, Ichigo initially suspects Ryou might be the Blue Knight because they both have blue eyes and blond hair, and both commented that she was heavier than she looked when they first carried her. Later, she suspects Keiichiro after noticing he has an injury in the same place as the Blue Knight's on the same day. As the final battle looms, it is revealed that the Blue Knight is actually an alternate persona of Masaya, Ichigo's boyfriend, created from his desire to safeguard her.
In the original Tokyo Mew Mew manga, the Blue Knight only appears sporadically to protect Ichigo—using an unnamed sword before vanishing shortly thereafter. After his true identity is uncovered, he joins forces with Mew Ichigo to fight alongside the other Mew Mews once before Masaya is exposed as their enemy, Deep Blue.
In the anime adaptation, the Blue Knight's role is expanded. He battles the Mew Mews multiple times and often advises them about the chimera animas' weaknesses while motivating them when they feel discouraged. The anime also shows Mew Ichigo using her "Ribbon Strawberry Surprise" attack to enhance the Blue Knight's strength to defeat chimera animas. In contrast, the manga depicts him single-handedly defeating both chimera animas and Kish.
The Blue Knight disappears from Tokyo Mew Mew when Masaya transforms into Deep Blue, except for Ichigo recalling him in a flashback following Masaya's death. In Tokyo Mew Mew a la Mode, Masaya mentions he no longer possesses the powers he had as the Blue Knight. Neither the manga nor the anime explicitly clarifies whether Masaya's Blue Knight abilities stemmed from the dormant Deep Blue within him or if they were his own powers.
In the anime adaptation, Megumi Ogata voices the Blue Knight. In the English adaptation of Mew Mew Power, Sean Schemmel provides his voice. (Source: Wikipedia)
