Deep Blue is the leader of the aliens and the primary reason they have returned to the Earth. Deep Blue went to sleep within the Masaya personality, leaving Masaya with no memories of whom or what he really was, though he retained Deep Blue's disgust for the way humans were treating the environment.
Unlike Masaya, Deep Blue is cold natured and cruel hearted. When he first emerges, he attacks Ichigo, cutting her arm. He also ignores Kish's plea that he not hurt Ichigo, determined to kill anyone who defies him. When Kish later challenges Deep Blue to a dual to protect Ichigo, Deep Blue kills him without any hesitation. Killing Kish enables the Masaya personality to temporarily re-emerge. Masaya is able to hold back Deep Blue when he tries again to kill Ichigo, then he releases the final mew aqua inside Deep Blue, which kills Deep Blue and himself but releases a healing force across Tokyo that restores Kish to life and heals the wounds of the Mew Mews, Ryou, Pie, and Tart.
Though Deep Blue is the series primary antagonist, he does not actually appear until the end of the sixth volume of the manga. In the anime series, however, he appears in the form of a blue light to whom Kish gives progress reports. In the twenty-sixth episode, after Kish brings him a bit of mew aqua, Deep Blue is shown in a shadowed version of his true form until his full awakening in the forty-ninth episode. Deep Blue's death is also changed in the anime, with Masaya still holding Deep Blue at bay, but it being Mew Ichigo who uses her finishing attack to kill Deep Blue and free Masaya.
To keep the true identity of Deep Blue a secret in the anime, he is listed in the original credits of the first two episodes as "Mysterious voice" with a question mark in place of his voice actor's name. After the second episode, he is listed by name, but the question mark remains in the voice actor's spot until the forty-ninth episode when his identity is revealed. At that point, the credits are changed to show that the voice actor is Megumi Ogata, who also voices Masaya and the Blue Knight.
Deep Blue is one of the few characters in the Mew Mew Power dub version whose name remains unchanged, however he is also changed from being a savior for the aliens to being a destructive force that wanted to destroy the Earth, which causes the others to turn against him. In the Mew Mew Power English adaptation of the anime series, he is voiced by Scottie Ray.