Sirenix

Sirenix is the second transformation of Season 5. It is water related and the Dragnix looked for this ancient power to fight the villain Aquila as their Believix powers were too weak underwater. In addition, they would need Sirenix in order to enter the Infinite Ocean. Selena and Caris also got the Sirenix power from Aquila, called Dark Sirenix which help them to swim faster with their tentacles instead of a bent and flexible seashell-shaped wings.
 * Previous Transformation: Harmonix
 * Next Transformation: Bloomix

Overview
According to Miss Faragonda in Return to Alfea, the Sirenix power is an ancient power that was born of the magic of the ocean and it will make the Dragnix more powerful underwater since their Believix power is less effective under the sea. She also mentioned that no one had acquired Sirenix for a long time.

Requirements
The fairies need to find the Gem of Self-Confidence, Empathy and Courage within one lunar cycle in the oceans that are all over the magic dimension, or they would lose their powers forever. After that, they needed to activate the source of Sirenix in Lake Roccaluce. Then the fairies' Sirenix boxes will appear along with their Sirenix Guardians, who combine their powers to open the portal to the Infinite Ocean. Finally, Omnia, the Supreme Guardian of Sirenix will appear with the portal to the Infinite Ocean which the fairies needed to cross into and they became Sirenix fairies.

The Witches can't be allowed to acquire Sirenix by the Sirenix Quest, as Selena and Caris, the only Witches known to have acquired Sirenix, obtained it after Aquila stole it from Aqua, and gave it to them.

Dark Sirenix
After Aquila forced Aqua to tell him where the source of Sirenix power was, Aquila headed to Lake Roccaluce to destroy the Source of Sirenix permanently, so Aqua can't protect her Sirenix from being stolen by him. After he destroyed the source (which was later restored by the Dragnix using their Harmonix powers and the powers of the Selkies), Aquila absorbed Aqua's Sirenix powers and used his trident to give a dark version of Sirenix to Selena and Caris. It's unknown how the witches still keep their Dark Sirenix even Aquila loses his power and trident.

Sirenix Clues
Sirenix Clues were riddles given to the Dragnix to find the gems of Self-Confidence, Empathy and Courage.

Aquaria
With every twist and turn, deeper you go until the Shimmering Shells sing with the ocean's voice.

Lighticia
Venture where the dark depth of the ocean shine, a precious gem self confidence, lies in the deeps.

Ignisia
Like a shining ruby under the sea, corals are strings that you feel in a key.

Tenzo
''The Winx had to understand the message in the moon Reef's music. It lead them to Databridge Castle in which Aqua, Miu and Doori have unity.''

Alynguard
''Find the Dark of the Depths. It only answers to courage.''

Orochidia
Find the Green Reef and snatch courage from it's jaws.

Special Sirenix Spell/Sirenix Power
Just like each Fairy has a special Believix power, now they each have a special spell/attack that they must master: during the course the will each have a special task which this power is needed although some are attacks other are abilities that use powers that are not meant for attacks but rather for purifying such as Miu's spell which was used to turn the singing whales back to their pure form.
 * Doori: Light of Sirenix
 * Miu: Dragon of Sirenix
 * Aqua: Water of Sirenix
 * Azami: Moon of Sirenix
 * Tsukiko: Galaxy of Sirenix
 * Hyang: Phoenix of Sirenix

Sirenix Wish
On gaining Sirenix, a Fairy is given a wish which she can ask her Guardian of Sirenix to grant it once she has accomplished the purpose for which she acquired Sirenix.

Sirenix
The hair mostly stay in ponytail, with highlight streaks and the hair changes its colors when they go underwater. Their outfits consists of a sparkly mermaid skin top, a belt, mermaid skinned colorful leggings with tail fins and boots with ribbons wrapped around them. The girls also have bracelets made of a piece of jewelry, flower or marine creatures and strips of cloth wound around their arms, and a piece of jewelry in their hair. The wings are in seashell-shaped. Like the previous fairy powers, Sirenix has a special effect: When the fairies flutter their wings, the water bubbles will be formed with the theme colors of that fairy.

Dark Sirenix
The outfits consists of a body suits that is less revealing and darker than Sirenix, a pairs of stiletto, a glove made of the same material with the outfit cover a hand and even the socks covering the girls' legs. They wear smeared makeup on there eyes and lips. The hair mostly stays in ponytail or pigtails. Instead of seashell-shaped wings they gain tentacles.

Gallery
Main article: Sirenix Gallery