The Think that i love about the mermaids in Lost Voices, is that they are technically dead.
I hate to make the vampire connection with mermaids but if any of us have seen Interview with the vampire I am consistently brought to the scene when Claudia Dies and become a vampire. she becomes a dazzling enthralling little creature akin to a porcelain doll

The Girls in Lost voices are similar. even though their bodies kinda turn to water and this make them mermaid it only happens because they reach a point where they are close to death and losing their lives but too strong to die. The shimmer that surrounds the girls heads tells stories of their tragic lives and their near death. you can even seen physical forms of their lives and near deaths. one of the mermaids that luce notices has a slight twist to her neck or something like that and others have the ghost of scars and such from what i gather. Its an interesting ideal to go with. and it hearken back to the stories of mermaids being the souls of woman who dawned at sea or unbaptized babies or woman who died unmarried and stuff like that. and it also give the story a very dark and kinda twisted vibe and i love it.