The Blue Knight (蒼の騎士, Ao no Kishi) is an unknown male who is introduced at the end of the fourth volume of the manga. During a battle with Kish at an aquarium, Ichigo is in danger of losing when the Blue Knight appears and rescues her. The Blue Knight tells Ichigo that he "is hers" and that he was "born to protect her". During the rest of the series, Ichigo initially suspects Ryou of being the Blue Knight due to both having blue eyes, blond hair and their both saying that she is heavier than she looks the first time they carried her. She later suspects Keiichiro of being the Blue Knight after he turns up with an injury in the same spot as the Blue Knight on the same day. As the final battle of the series approaches, it is revealed that the Blue Knight is actually the alternate persona of Ichigo's boyfriend, Masaya, created out of his desire to protect her.
In the original Tokyo Mew Mew manga, the Blue Knight initially appears only as needed to protect Ichigo—fighting with an unnamed sword and disappearing soon after. After his true identity is revealed, he goes with Mew Ichigo to fight together with the other Mew Mews once before Masaya is revealed to also be their enemy Deep Blue. In the anime series, the Blue Knight is given a larger role, fighting with all of the Mew Mews several times. In addition to fighting, he would often advise the Mew Mews of the chimera animas' weak points and encourage them when they feel like giving up. The anime also depicts Mew Ichigo using her "Ribbon Strawberry Surprise" attack to boost the Blue Knight's attack in order to defeat chimera animas,[episode needed] while the manga shows him defeating both chimera animas and Kish single-handedly.
The Blue Knight disappears from Tokyo Mew Mew when Masaya transforms into Deep Blue, except for Ichigo remembering him in a flash back after Masaya's death. In Tokyo Mew Mew a la Mode, Masaya notes that he no longer possess the powers he had as the Blue Knight. Neither the manga nor the anime clearly states if Masaya's Blue Knight powers came from the sleeping Deep Blue within him, or if they were his own powers. In the anime adaptation, his voice actor is Megumi Ogata. In the Mew Mew Power English adaptation he is voiced by Sean Schemmel.