Rina Touin (洞院 リナ Tôin Rina) is a main character in Mermaid Melody. She is currently dating Masahiro Hamasaki. She is a Mermaid Princess of the North Atlantic ocean and works to defeat the Dark Lovers and Mikeru's Servants. Her name is often pronounced or translated "Lina". However, her official name is Rina. Her palace was destroyed by Gaito, Awhile later, Her best friend was originally Noel until Noel got captured by Gaito. Because of this, a rumor was spread that Rina abandoned Noel and let her get captured. Rina felt very guilty because of this. This was one of the reasons why she wanted to defeat Gaito.
- Karen - Karen held a grudge against Rina because she believed that "Rina Abandoned Noel". Because Noel is Karen's older sister, even though they never met, she cared deeply for Noel. When she heard that Noel was captured she blamed it on Rina. The truth was that Rina was going to be captured by Gaito, But Noel saved her and got captured instead. Later in the series she finds out the truth, and that this was a misunderstanding. Karen no longer dislikes Rina.
- Lucia Nanami - Lucia is one of Rina's Best Friends. When Lucia first met her (Rina was walking to school) she thought Rina was a man because of her masculine body, and because she was dressed in a Boy School Uniform. When Lucia first talked to her, Rina ignored her. After that, Lucia promised to herself that she would become friends with Rina. The next day, Lucia followed Rina to the roof of the school. She mistakenly though that Rina and Kaito were on the roof kissing, all though they were just standing in a strange position talking. Lucia, was now in a state of sadness.