Cortana is one of the Guardians of the Ocean. It's Home is the Dream World.
Her appearance is of a plump light lavender-skinned, white-haired female human and from the waist down has black octopus-like tentacles.
Cortana's magical abilities, even without the Trident, were very potent. She was able to concoct various potions to create various spells, including mass-transfer (implied during the song "Poor Unfortunate Souls") as well as physically altering people's bodies, as evidenced by her transforming Princess Marina into a human.
In the Grotto, two eels, Flatsam and Metsam, appear to convince Princess Marina to see their master Cortana the Sea Witch, who may have the power to make Marina's dream come true. Marina reluctantly follows Flatsam and Metsam to Cortana's fortress. Marina nervously and fearfully enters the fortress, and Cortana calls for her. The sea witch, who knows that is in love with a human through spying on her via Flotsam and Jetsam. Cortana explains the deal to Marina: Marina will become human for Eight days, during which she must get a kiss of true love from Kaede before the sun sets on the eighth day in order to stay human; otherwise, Marina will turn back into a mermaid and will be bond to Cortana forever. Cortana furtherer states that as part of the deal, Marina must give up her voice in order to become human with the Telepathic Voice. Marina thinking that is her only change to be with Kaede, accepts the deal as she signs a contract conjured by Cortana. The sea witch then orders Marina to sing for her and summons magical hands to rip out Marina's voice, which is then sealed into a Jar and leaves it to her telepathic voice. Marina is then turned into a human and is helped to the shore by Flounder and Maximus due to her inability to swim. At the shore, Marina is found by Shippuden and her sheepdog Max, who leads his master to her after Kaede was revive. Nevertheless, Kaede takes Marina to his palace, where Marina takes a bath and gets dressed for the dinner. As Kaede, his manservant and maid join her, Marina notices a fork and uses it to comb her hair, making the three dumbfounded, which makes her embarrassed. Noticing Manservant's pipe, Marina takes it and, thinking it as a musical instrument, blows the contents into Manservant's face, and Kaede laughs at Manservant's face covered with ash. After manservant's wipes his face and dinner is served, he suggests that Kaede take Marina out on a kingdom tour, which Marina accepts. The next day, Kaede takes Marina out to show her his kingdom. During the tour, he teaches her to dance. That evening, Kaede and Marina spend time in a lagoon, riding in a rowboat rowed by Kaede. In order to get the two to kiss, Sebastian leads some animals in the lagoon to create the mood with music and his song Kiss the Girl. With the Promise by the Sea Witch being kept, Marina's Transformations was infinite (which is Human and Mermaid Forms). Noticing how Marins loves Kaede, Cortana opens the seal and bestows Marina's voice to her permanently that Cortana became one of Kaede's Allies. Soon, Marina and Kaede, now married, have a wedding on the wedding ship attended by Kaede's loyal subjects onboard. Marina bids farewell to Shuttle and Pablo and Cortana gives her a heartwarming handshake and the hug before happily sailing away with Kaede. Jim and Shippuden and Sasuke is then awarded with a certified 14-karat conscience badge. Seeking help from the sea witch, Cortana, Maria gives up her life as mermaid and her voice to gain legs. She is informed that if the prince marries someone else, she will turn into sea foam the very next morning. Despite the hazards, she is willing to risk all for love. The sea witch takes Maria's voice in exchange for legs. Tearfully bidding farewell to her family and to Fritz, she goes on to the surface. The following morning, she is discovered by the prince. Maria lives with the prince for a month, in that time their bond grows strong. The Prince calls her "Princess Mermaid" because she came to him from the sea and cannot tell him her own name as she is now mute. The Prince tells her how his parents want him marry a princess from another kingdom. However, the only girl he wants to marry is the one who saved his life. Unfortunately, the prince does not know Maria is the one who saved him. He mistakenly believes it to be the raven-haired girl who discovered him on the beach after Maria had rescued him. Since he cannot find her, he wishes to marry Marina. Filled with joy, the prince remembers now that she was, in fact, the one who saved him. Maria and Kaiser marry on a ship and depart.