Syrena

Syrena is a character from Pirates of the Caribbean: On Stranger Tides portrayed by French-Spanish actress Àstrid Bergès-Frisbey. She is a beautiful, enigmatic mermaid who swims against the tide of her more lethally-minded sisters of the sea.

Background information
Mystery surrounds the mermaid Syrena, even down to her true name, for “Syrena” is only what she’s called by missionary Philip Swift during her captivity by Blackbeard. After her fellow mermaids attack Blackbeard’s crew at Whitecap Bay, Syrena and Philip begin to recognize a quality in each other that draws them together, allowing them to become allies against a common enemy in Blackbeard. Each discover more of their true beings, but risk their lives when they listen to the sounds of their hearts.

On Stranger Tides
In the aftermath of a battle between Blackbeard's crew and mermaids, the currently-unnamed Syrena was captured as a mermaid's tear was needed for when they reach the Fountain of Youth. During the jungle trek, young missionary Philip Swift notices that she can not breathe and he opens the glass tank a little to allow air to flow through. When the glass coffin Syrena is being carried in breaks, the mermaid changes to a human form, causing Philip to remove his shirt and cover Syrena's naked body. Philip then carries her the rest of the journey due to her inability to walk and names her "Syrena" in an attempt to make Blackbeard realize she is a person and not a creature as he used to call her.

By the time Syrena was threatened to present a single mermaid's tear, Philip and Syrena develop a strong bond and eventually they fall in love. Blackbeard exploits this by apparently killing Philip, and later revealing that he is alive, and using it to obtain Syrena's tears of joy. Having acquired the tear, Blackbeard's crew left Syrena staked out to die, but a mortally wounded Philip later returns to cut her loose. Now free, Syrena swims off into the pools, where she found the Chalices needed for the ritual at the Fountain of Youth. Syrena returned the Chalices to Jack Sparrow, saying "Do not waste my tear" before swimming away.

As an injured Philip tries putting water on his wounds, Syrena returns and offers to save him. But the missionary only asks for her forgiveness. Syrena then gives Philip a mermaid kiss, which is said to prevent one from drowning, and pulls him underwater with her as they swim off together through the pools to freedom.

Trivia

 * Syrena is inspired by Ariel, another mermaid from The Little Mermaid. Syrena and Ariel share a couple of similarities. Both save a human, fall in love with him, and have their tails turn into legs to walk on land.
 * Her fellow mermaids (sisters) are like King Triton and his daughters from The Little Mermaid.
 * Astrid Berges-Frisbey did not speak any English when she was cast. She was tutored on-set by co-star Penelope Cruz.
 * The character and abilities of Syrena were previously seen in another Disney film: Splash!  Its mermaid protagonist Madison is also able to grant a human being the ability to breathe underwater, so long as this human remains with her. This power contrasts the traditional "undine's curse", which in folklore allowed a mermaid to cause an unfaithful human lover to drown in his sleep (a possible classical explanation for the condition known as sleep apnea). Additionally, both Madison and Syrena share the quality of their tail transforming into human legs, when dried (and vice-versa when wet).
 * On days off, Syrena's portrayer could not go swimming in order to stay pale for the role.

Quotes

 * "I cannot."
 * "I do not ask for help."
 * "Deadly ? No."
 * "No. You are different."
 * "Are you not ? You protect."
 * "All die, even you. Soon I hear."
 * "Philip, you're alive!"
 * "You came for me. Why?"
 * "Do not waste my tear."
 * "You're hurt."
 * "Me?"
 * "Philip, I can save you. You need only ask."
 * "And what is that?"
 * "Ask."