"Pichi Pichi Pitch: Mermaid Melody" is one of those manga series that seems like it should be for 'tweens, especially considering the target audience of the anime series. This manga series, however, is not like the anime series and has more sexual themes than I imagine most parents would like for their 'tweens (an additional story in the last volume is titled "Get Nude," if that helps).
Mermaid Melody is a re-telling of the Little Mermaid ... sorta. In this version there are seven mermaid princesses that each represent the seven seas of the Earth. Some cataclysm has struck which has caused some of the princesses to go missing. The remaining princesses are sent to the land to figure out what happened so they can gather all of the princesses together to summon the Goddess "Aqua Regina." The story centers around, Lucia the pink Mermaid of the Pacific (If I remember correctly). She rescued a human boy, Kaito, when she was little and finds him again on land. Kaito is looking for the mermaid that rescued him because she is his first love. Lucia can't tell him it's her because she will turn into bubbles if any human discovers her identity. All of this is woven together with some Sailor Moonish villains that try to attack the mermaids and humans with bad singing. The mermaids fight back with singing of their own, led, of course by Lucia.
The manga series is much deeper than the anime series, which I found pleasantly surprising. Mermaid Melody isn't for everybody -- to be honest, I can't say who this was aimed at since it's more adult than would be appropriate for 'tweens. The singing and the silly side stories really threw me off. Anyhow, I give this 3.5/5 for a relatively enjoyable manga series with nice pretty pictures.
