Season 5

In the kingdom of Andros, Aisha's uncle Neptune plans to make his son Nereus a prince, Nereus's twin brother disrupts the crowning ceremony and is sent to prison.

The Winx change their concert, into a benefit to help clean up the oil spill. Meanwhile Tritannus escapes from jail with the help of the Trinx and begins absorbing the oil spill's pollution and slowly begins transforms into a monster.

The girls all head back to Alfea to talk more with Ms. F and read up o a book called The Sirenix. While in the library they are attacked by both the Trinx and Tritannus: who is getting stronger. Sky takes a hard blow to the head.

Krystal attempts to heal Sky's memory, but the memory of losing the pendant of Eraklyon is causing the blockage, but only Sky knows where it can be found. Timmy helps Tecna update her phone to find the Sirenix Book, which the Trix secretly sabotage. While, searching for the Sirenix Book, the Winx find the fake one, which turns Tecna into a terrifying robot, whose mission is to find the Sirenix Book.

The Trix return and the Winx are back at Alfea for training. Ms. Faragonda calls the Winx in and tells them about the Lilo, a magical plant which is on the verge of blooming for the first time in centuries, and it is somewhere on Earth, in Gardenia. Unfortunately, the Trix are searching for the Lilo as well to strengthen their own powers. The Winx find that the Lilo is in the possession of Macy, Mitzi's little sister. The Winx try to stop the Trix from gaining the Lilo and prevail with everyone believing in them once again, making their Believix powers stronger.

The Winx Club try to find the creature of the Rainbow Mantle to earn the boon of the Ancestral Spirit of Nature. The Trix attack Stella, Musa, and Tecna, and Bloom, Flora, and Aisha defend them. Bloom saves a horse, who reveals itself to be the Creature of the Rainbow Mantle when the Trix try to attack it. It heals the Winx, and they win the competition. Upon opening the Sirenix Book, they are given Sirenix guardians and learn they must earn Sirenix before the next lunar cycle ends. To begin their quest, they must first find mystical gems known as the Gem of Self-Confidence, the Gem of Empathy, and the Gem of Courage. The Sirenix Guardians grant them a new transformation, Harmonix, to help them with their quest.

Trying to obtain the Gem of Self-Confidence, Aisha, Stella and Flora search in the oceans of Stella's home world, Solaria. Meanwhile, the Trix and Tritannus' mutants attack Gardenia to get more toxic pollution for Tritannus to be even stronger and more powerful. Bloom, Tecna, and Musa appear with their new Harmonix powers and stop them. In the end, the Winx obtain their first gem.

Tritannus raids King Neptune's underwater palace and transforms his entire family into mutants. Then he absorbs the power of his dad's mystical sword. Meanwhile, Musa, Aisha, and Stella get a second clue to Sirenix which leads them to Musa's home world, Melody. Searching for the Gem of Empathy, Tritannus transforms Musa into a monster and she is saved when she bonds with the Selkie who guards Melody's ocean gate, Sonna. Meanwhile, the Trix and Tritannus reach Daphne in Lake Roccaluce, and capture her.

An age-changing spell causes Stella to become a three-year-old girl. Musa, Flora, and Brandon look after her. Eventually, the spell wears off, reverting Stella to her actual age and appearance. Meanwhile, Bloom, Tecna and Aisha go to Tecna's home world, Zenith, to find the Gem of Empathy. Aisha and Tecna get into a fight and Bloom stops them as they have to work together to obtain the second Sirenix gem. They do so, and they gain the Gem of Empathy, leaving only one more challenge to gain the Gem of Courage.

Bloom plans to go home for Christmas, but the Trix cast a spell that creates ice monsters and turns the magical protection barrier against them, trapping them at Alfea. The Winx Club fights the Trix and try to make Bloom feel at home to which she gives them her gifts and calls them the best friends. After this the Trix reveal themselves, and destroy the gingerbread house.

Red Fountain is having a scooter show. The Trix make themselves invisible and turn the scooters into a type of lion demon. The lion demon's power is far much stronger than the Winx's Harmonix. Sky has an idea on how to break the spell, and the lion demon's turn back into scooters. After the race, Flora, Musa and Stella go to Linphea for the test of courage. Bloom and Sky go on a date and are ambushed by the Trix. The Winx end up saving them.

The Winx Club, excluding Musa and Tecna, head to Domino, Bloom's home-world, for the celebration of its restoration. But when Bloom discovers that the last and third gem is somewhere in Domino's ocean, she and her friends must leave the celebration immediately.

Tritannus and the Trix steal Daphne's Sirenix powers and gives it to the Trix as Dark Sirenix. Meanwhile, the Winx Club has collected all three gems of Sirenix, but they had to find the Source of Sirenix to complete the quest; they successfully find the source at the bottom of Lake Roccaluce and obtain the Sirenix power, and they enter the Infinite Ocean. Omnia, the Supreme Guardian of Sirenix, tells them they each get a wish but after they have pleased destiny. Tritannus has all of the Selkies' powers, and together with the Trix, he enters the Infinite Ocean as well with Daphne still his captive.

The Winx find an island composed completely out of trash, which Tritannus uses to refuel in toxins. The Winx arrive and stop the Trix, causing them and Tritannus to retreat. After following Tritannus and the Trix into the Infinite Ocean, Aisha is heartbroken to find the royal family of Andros' underwater kingdom mutated into demon sea monsters.

Tritannus plans to activate the Emperor's Throne; the Winx must restore order when Tritannus takes the seal from the Pillar of Light. The whole of Magix is plunged into darkness. Solaria is the most affected, especially King Radius who gets sick because of his connection to the sun. The Winx Club goes to the Infinite Ocean to restore the Pillar of Light. Stella succeeds in gaining her Sirenix spell, The Light of Sirenix, which sends Tritannus' mutants packing. Bloom attacks Icy, which causes Tritannus to get angry and attack Bloom and Aisha.

As darkness envelopes the magical worlds, everyone looks to Stella to help save them and her father's life.

Daphne urges the Winx to look for the eye of inspiration, but they don't know what it is or where to find it. On Earth, Tritannus turns the garbage island into a ravaging monster that causes panic in Gardenia. The Winx Club need to stop this catastrophe before it is too late.

Tritannus takes control of a dangerous fish called the Devourer and orders it to devour all of the Selkies in the Infinite Ocean. Flora, Tecna, and Musa must then try to find its weakness point. On the world Domino, a royal council meeting is held on what action must be taken about Tritannus. But it seems that all of the kingdoms have different ideas and different points of views.

Tritannus takes the Seal from the Pillar of Balance, causing everything in all of the worlds to become dangerously unstable, and shake up and fall apart as the result of Tritannus tampering with the second Pillar. Musa's home world's singing whales that keep Melody in balance suddenly disappear. And the Winx Club must fight both Icy and Tritannus as Darcy and Stormy are missing.

Darcy and Stormy show up with the Singing Whales of Melody. Icy is not impressed and rather be with Tritannus. Much their dismay they send the whales after the Winx causing a horrible sound. The Winx try to attack but are stopped by Musa, who uses her Sirenix spell, the Voice of Sirenix, to free the singing whales. Then they use Sirenix convergence magic to restore the Pillar of Balance.

The Winx Club and the Specialists plan a real date for Tecna and Timmy in Magix City. The Winx head for the Pillar of Control before Tritannus, and Bloom is informed by Daphne that the seal of the Pillar of Control must be destroyed so Tritannus will never attain its seal to activate the Emperor's Throne. The Winx go to the Infinite Ocean, but are attacked by a giant electric eel. Realizing they need Tecna's aid, Musa contacts her; and Tecna goes to help her best friends. Using Aura of Sirenix, Tecna defeats the giant eel. Tecna later returns to Timmy and they share a moment together and come to realise that it is indeed nice to spend time together.

The Winx play a volleyball game then Krystal wins and Winx lose. Tecna then gets a message from the king of Zenith that they will not join the alliance and the Winx head to Zenith to sort out the matter. Tritannus finds out what the Winx did with the seal and gets very angry and he attacks the pillar causing all technology to run out of control. The Winx transform to stop the problem from getting worse. After an intense battle Flora uses what she learns to stop the attack and Tecna convinces the king to support the alliance.

Bloom learns the story of Daphne and Politea and how they were cursed by the Ancestral Witches. To protect her friends from the Sirenix curse, Bloom and Serena go on a mission to find the Shark's Head, where Politea lives. However, they and Icy fall behind when Darcy and Stormy drain Politea of her Sirenix powers.

Tritannus leaves an acid rain in the beautiful waters of Paradise Bay, where dolphins swim free. To prevent an environmental disaster, the Winx must find the Breath of the Ocean. The Winx are attacked by big insects, and Flora finds the Breath of The Ocean. Tritannus and Icy are attacked by the Specialists and their allies and try to escape, but are confronted by the Winx. They escape and Flora uses her special ability, the Flower of Sirenix, with the Breath of the Ocean, and restores Paradise Bay. She earns her Sirenix wish and wishes that the people of Earth would care for the planet more.

Helia and Flora are still on the rocks, with Flora mad at him for his actions. After a ballet they make up. A call from Aisha's cousins leads to a battle between Bloom and Tritannus, and Selkies versus mutants at the Pillar of Light with Aisha caught in the crossfire: the Fairy of Waves loses her Sirenix energy to Tritannus, who intends to use them to fully activate the Emperor's Throne.

After finally managing to activate the Emperor's throne, Tritannus is losing control of his powers and himself, and even turns against Icy. One final showdown takes place between the Winx Club and Nereus to save the magical universe. In the end, Tritannus is defeated by Bloom and Nereus and banished to Oblivion for his actions. Bloom then made her Sirenix wish to break the Sirenix curse forever, thus restoring her big sister Daphne's physical body after so many years as a ghostly spirit.