Winx Club Forever
It is a harp-like coral found in the Ruby Reef, which can be played whenever its strings are plucked.
In the "Secret of the Ruby Reef", where the Winx go in the search for the gem. It reminds Musa of her past and time she spent with her mom. After she, Stella and Aisha used their Harmonix, Tritannus - who had forced his face through the Ocean Gate of Melody by absorbing the powers of Sonna, appeared and tried to turn Aisha into an monster, but Musa jumped in front of the ray and got turned into a monster instead.
Being chased by Musa through the ocean, Stella and Aisha hid in an cave and Lemmy got an idea of making Musa bond with Sonna to restore her to her original form. While Stella distracted Musa, Aisha got Sonna along with Lemmy.
Sonna and Musa met rather dramatically and suddenly but Musa got her original form back and Sonna got her powers back. After that, they traveled nearby to the Ruby Reef and Musa found the coral harp and played her mother's song.