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 and Princess 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 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 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 Silva carries a clone of Undine to the town, and the clone erects a protective barrier around the town. Once the mission is over, 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 Vermillion for a bath.At Elmora Lake, Undine watches over the three women as they bathe.
- 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|
|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|
|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|