A Sirenix Box is needed to acquire Sirenix transformation, many fairies before Winx like Daphne gained their own Sirenix Box. After finding the Sirenix Book in the previous episode, Tecna and Aisha want to open it, but it won't open. They must complete quest for one lunar cycle or they will lose their power. Then, they must find Creature of the Rainbow Mantle to get a new power. After finding it, they must find Gem of Self Confidence, Empathy, and Courage, which are hidden somewhere in the vast oceans of the Magic Dimension. Then, they gain the Sirenix. Tecna, Flora, and Musa set out to find the Shimmering Shells in the simulation chamber while, the rest (Bloom, Stella, and Aisha) find the hidden cove in Andros with their new Harmonix power. Stella is one to find Gem of Self Confidence from the shield, that was hidden into Royal Deeps of Solaria.
They have a lead for Gem of Empathy by following an riddle Musa's mother left to her daughter long time ago which leads them to Ruby Reef of Melody. This riddle leads them to Zenith, where Gem of Empathy is located.
Tecna is the one to find the Gem of Empathy but it takes the convergence of Tecna, Bloom and Aisha for them to get the gem.
By next riddle, they try to find Gem of Courage from Linphea and they eventually receives another riddle, leading them to Domino, where Bloom gains Gem of Courage from jaws of giant and dangerous fish.
After Winx went to Source of Sirenix and used their Sirenix Boxes to get the transformation, boxes were no longer needed.