|The Lonesome Princess|
|Air Date||April 26, 2003|
|Previous episode:||Next episode:|
|Swaying Thoughts||An Icy Kiss|
"The Lonesome Princess" "Kodoku na Ōjō" (孤独な王女) is the 4th Episode of Mermaid Melody Pichi Pichi Pitch.
A new sea monster, Yuri, appears during a concert given by Taro Mitsuki and uses her music to hypnotize the attendees and attack the mermaid princesses, who are also there. Rina Tôin reveals herself to be a mermaid princess and joins Lucia and Hanon in the end.
Lucia was given two concert tickets from Hanon for her and Kaito to enjoy something together. The next day, after Kaito went surfing, he is met up with Rina who coldly tell Kaito about his house and his dead parents which Kaito say it has nothing to do with her, when Rina grab his shirt and asked how long is he going to play innocent. Kaito did not understands but Rina kept on demanding the truth of him. Kaito then yelled at Rina that he won't forgive her if she contiues to falsely accuse him. Lucia saw the two and believe that she was wrong about Kaito and Rina liking each other and then went back to hide. Rina then look at Kaito intensely and a flash of Gaito appeared in her mind. Rina then ran away from him and Kaito then walk to his house and saw Lucia sitting on the door step. Lucia was then invited to Kaito's house to fix Kaito's shirt that has a loose button. Lucia then poke herself so Kaito put her finger into his mouth. Lucia then accidently hit a remote that plays Kaito's father's song. Kaito then turns off the music and give Lucia one of her friendship rings that he found on the roof of school in the last episode. Kaito then claims that he does not understands girls. Lucia then remember the tickets and invites Kaito to the concert which he agrees. However neither both of them know that Rina is secretly easdropping on them. The scene shifts to Gaito's castle showing Gaito gazing at Noel sleeping in the glass tanks. He then tell the Dark Lovers to capture the remaining princesses and to bring them to him quickly so that he can summon Aqua Regina and control the whole ocean while taking a sip of his wine. Yuri that appeared and asked if Gaito like the mermaid princess that they both capture which he anwser is yes and that Yuri did a good job. Yuri then inform that she is close to find the other mermaid princess that had escaped from them and she then taught Izuru and Eriru on their failures to capture the remaining princesses. She then brags that she will catch the other princesses and their pearls. The scene then shifts to Rina sitting on the beach. She then open her shell locket to reveal her green pearl and start to think about what had happen with her in the sea. In her flashback she remember she was traveling with Noel and that they need to find the remaining princesses until Gaito and Yuri caught up to them. Yuri then made water ropes to catch Rina but before that could happen Noel pushed Rina away and got caught instead. Rina then told Noel that she will save her but Noel told Rina to escape before she will pulled away from Rina, leaving Rina yell her name before was forced to get away. Rina then closed her shell pendant and continue to sit at the beach a little more. Lucia and Kaito are then seen sitting to listen to the piano played by Tarou. Kaito was about to leave when Hanon (came to see Tarou) ask Kaito to take Lucia with him who was sleeping. Kaito then brought Lucia out of the concert when Kaito stop when he saw Rina standing in front of him.
- This is the first episode when Yuri appeared in the series.
- This episode shows Rina's past with Noel.
- In this episode, it is revealed that Rina is a mermaid princess. Her idol form is revealed and she teams up with Lucia and Hanon.
- In the end, Rina apologizes to Kaito after finding him suspicious. She also befriends Lucia and Hanon as she wears the friendship ring that Lucia made.