Syrena is the love interest to Philip Swift in Pirates of the Carribean: On Stranger Tides.
Syrena (as Philip named her, since mermaids don't seem to have names) is a mermaid who lives near the island containing the Fountain of Youth. While most mermaids are assertive and sure of themselves, Syrena is quite timid.
Syrena first met Philip during Blackbeard's raid on her mermaid colony, as he requires a mermaid's tear to use the full properties of the Fountain of Youth. She saved Philip's life at one point, only to be trapped by some rubble and cornered by Blackbeard's pirates. She is then put in a glass container and carried across the island. Phillip notices that the container doesn't let any air in and prizes it open. His compassion noticed by Syrena. When the container is broken and Syrena touches land, her tail transforms into legs. As she is not used to walking or even standing, Philip carries her.
Blackbeard notices that Philip and Syrena are growing closer. Her then tries forcing her to shed tears by threatening Philip's life, but mermaids are apparently indifferent to people dying. He then stabs Philip and dumps his body in a ditch, but purposely missed his vital organs. Philip recovers and goes to Syrena, who is so relieved to see him that she shes a tear. Blackbeard's men then pin her down and take the tear in a vial before tying her down and leaving her to die of dehydration, with Philip being forced to journey with him.
Philip escapes during a battle between pirates, the Navy and the conquistadors, making his way back to Syrena, he finds her barely alive. Mortally wounded himself, he frees Syrena but tells her to give the Jack Sparrow the chalices required for the Fountain of Youth's ritual. Syrena complies before coming back for Philip. She offers to heal Philip, who is moments from death. Syrena then kisses Philip and drags him underwater.
- Mermaid's prey on men's lust. Since Philip was a devout Christian, he was able to resist their physical charms. Syrena may have in fact picked up on this and manipulated his good nature so she could drag him underwater.
- Syrena's name comes from the Syrens of Greek mythology, whom the mermaids of modern mythology are based on, and Serenity, due to her passive nature.