Kala used to be Lagoona's best friend when they were younger, but when she saw all the praise and affection Lagoona got from her family when they showed up for her performances compared to how her father, the Kraken, was feared by the people of the Great Scarrier Reef and thus could never come to watch her, she became jealous and intentionally tripped up Lagoona during one of her dance performances, resulting in Lagoona becoming riddled with stage fright at the thought of performing again and being laughed at. Kala was also forced to live on her own, away from her father because of people fearing him and the shame she felt about it.
When Posea Reef, daughter of Poseidon, brings Lagoona back to the Great Scarrier Reef to help her overcome her stage fright and Kala's bullying, Kala sees another chance to humiliate her and gets the help of her best friend, the two-headed sisters Peri and Pearl Serpentine, to assist in this endeavor.
Later, when it is time for Lagoona to perform for the people of the Great Scarrier Reef in the Siren of the Sea competition, she suffers another panic attack and faints. Kala seizes the chance to laugh at her and encourage the crowd to do so as well, but when Gil and Lagoona's friends, who Posea had unintentionally brought back to the Great Scarrier Reef with Lagoona, defend Lagoona, explain recent events, and encourage the crowd to support her, Kala, enraged that her plan backfired and jealous once more, especially when yelled at by Lagoona's father, whom she retorts back at that he's not her father, emits an ear-piercing scream that summons her father, the Kraken, and goes after Lagoona in revenge, while berating her for stealing her glory.
Despite Posea quickly sending Lagoona and her friends back to Monster High, Kala and her father follow them, and begin to lay waste to the school, before Lagoona is able to climb onto the Kraken and confront Kala, who breaks down when she reveals that she only bullied Lagoona because she had been bullied herself in regards to her appearance. Once Lagoona tells her that Monster High accepts all monsters, regardless of their flaws, and she won't be ridiculed like back in the Great Scarrier Reef, Kala has her father stand down and fix the damage he wrought on the school, admitting that she was so upset over how the Great Scarrier Reef lived in fear of her father that she moved away to live separate from him. She realizes that she was wrong for not telling the truth about him and for bullying Lagoona, and Lagoona forgives her, restoring their friendship. Kala, her father, and Peri and Pearl, join in the celebration that follows by the Monster High swimming pool.