Undine takes the form of a beautiful woman whose long hair and gown are made of water. She has fish-like fins in place of ears. Undine has blue eyes and and pale skin that almost looks blue.
At first glance, Undine is smug and condescending; however, in reality, she is motherly doting. She acts very similar to her fellow spirit, Sylph.
Undine forms a contract to serve as protector of the newly-formed Heart Kingdom. The spirit is passed down to each generation of princess, allowing the princesses to inherit the power and knowledge of the previous generations.
Lolopechka and Undine fight Vanica Zogratis of the Spade Kingdom's Dark Triad and the devil Megicula when they infiltrate the Heart Kingdom. As a result, Lolopechka is cursed, which dismays and angers Undine. The Spirit Guardians and Undine keep Lolopechka's curse a secret from the citizens.
Undine and Lolopechka watch as Asta enters the Heart Kingdom. Along his journey, Asta is kidnapped in a ball of water and brought before Undine and the Princess. Undine creates multiple armored knights to attack Asta, but he uses his black form and Black Hurricane to cut through them all. Laughing, Undine traps him in a whirlpool and then tries to drown him by manacling his wrists and staking them to the floor. Secre Swallowtail dives underwater and releases the manacles, and Undine is surprised by Secre's Sealing Magic. Undine shouts when Asta heads toward Lolopechka's room.
Asta's sudden entrance startles Lolopechka, and she accidentally headbutts him. Undine pulls the boy away and comforts the Princess. When Asta mentions that he is searching for information on a devil's curse in the country, Undine reflects that they are unable to talk about it, but Lolopechka blurts out that she has the curse, much to Undine's shock. Undine then reveals that the curse is from Megicula and that they were testing Asta and the others in order to take on Megicula.
Suddenly Lolopechka breaks off from the discussion to handle various tasks around the kingdom. Undine grabs the Princess and dresses her in her formal attire, which causes her to trip and stumble. Undine tells Asta and Secre that the kingdom cannot afford to lose Lolopechka and then reveals that Megicula is in the Spade Kingdom. The group moves to the Princess's Palace and wait for Gadjah and the other visiting Magic Knights to arrive. When Lolopechka introduces herself, she trips over her dress again. Undine lifts the Princess back up and helps her to her throne. Undine then listens as Lolopechka discusses an alliance with the Clover Kingdom.
Six months later, one of Undine's clones along the border of the Heart Kingdom observes a Candelo moving through the Grand Magic Zone and relays the information to Lolopechka. When the Princess sends the Magic Knights to stop the fortress and to free Tolon, Noelle carries a clone of Undine to the town, and the clone erects a protective barrier around the town. Once the mission is over and the Knights return to the Heart Kingdom, Luck Voltia, Leopold Vermillion, and Asta want to spar with Gadjah. Lolopechka also wishes to join the fight but Undine talks her into joining Noelle and Mimosa for a bath.
At Elmora Lake, Undine watches over the three women as they bathe. Afterwards they return to the Princess's underground chamber.
Lolopechka shouts for Undine when she senses Vanica and her Dark Disciples infiltrating the Heart Kingdom. The Princess creates a map showing the intruders' locations and dispatches the Spirit Guardians and some of the Magic Knights to combat the Dark Disciples and to protect the citizens. Anticipating an attack on the Princess, Undine powers up Mimosa's Magic Cannon Flower so that it can defeat one of the Dark Disciples with a single shot. Vanica follows the Disciple into the underground chamber. During the ensuing fight, Undine defends against Vanica's Red Beast, and after Lolopechka discovers the Dark Triad's plan, Undine merges with a large quantity of water to trap Vanica and dilute her Blood Magic.Secre attempts to seal Vanica, but Megicula's Decaying World spell weakens the arrays, allowing the devil to break free. Undine watches in horror as the devil binds Secre and destroys the Ludic Sanctuary, injuring Noelle, Secre, and Lolopechka. The devil also manages to curse Undine, who collapses and calls out weakly to Lolopechka. Vanica decides to take Lolopechka as a hostage in order to motivate Noelle to become stronger.
- Water Magic: As the spirit of water, Undine uses this form of magic to generate and manipulate water.
- Immense Magic Power: As a spirit, Undine possesses a vast amount of magic power.
|Gadjah • Potrof • Floga|
|Holy Fist of Love • Sea Dragon's Waterball • Holy Water Assassination Bullet • Death Dealing Sea Serpent • Sea God's Hammer • Sea Dragon's Roar • Climbing Coelacanth • Aqua Javelin • Tainted Culvert Wyrm • Surging Waves • Point-Blank Sea Dragon's Roar|
|Sea Dragon's Nest • Sea Dragon's Cradle • Sea God's Shield • Valkyrie Dress|
|Current of the Fortune River • Sea Serpent Twine • Qualle Operation • Aqua Curtain • Ludic Sanctuary|
|Adrian • Fluss • Francis • Lily Aquaria • Owen • Noelle Silva • Risacca Ondell • Solid Silva|
|Lolopechka • Undine|
|Salamander's Breath • Salamander's Claw||Fana • Fana (elf) • Fuegoleon Vermillion|
|Sylph's Breath • Spirit Storm • Liable Tempest • Spirit's Hushed Dance • Spirit of Zephyr||Yuno|