Kai is featured very briefly in the film. At the beginning, he is one of the few servants who remains within the castle by orders of the King and Queen of Arendelle when the castle is locked away from the rest of the kingdom. Kai can be seen aiding the couple prior to their ill-fated sea voyage. When the King and Queen perish in a storm, Kai and another servant are seen veiling the royal portrait.
When the castle gates finally open for Elsa's coronation, Kai introduces The Duke of Weselton to the royal siblings at the coronation's ball, but accidentally mispronounces his name as "Weaseltown", leading him to be harshly corrected by the Duke.
After Elsa finally returns to Arendelle and lifts the winter curse, Kai is made aware of Hans' fate by the French dignitary. Kai then informs the Duke that Arendelle will be cutting ties with Weselton permanently, made official by Elsa herself. Much to the Duke's dismay and irritation, Kai pronounces his kingdom as "Weaseltown" once again.
Kai is last seen in the film skating on Elsa's newly created ice rink with another servant.
In the featurette, Kai is first seen tending to Christmas preparations in the castle, when he receives a surprise visit from Olaf. He is later seen during "Ring in the Season", as Anna and Elsa prepare to bring in the Yule bell to kick off the holidays. Near the climax, Kai, Anna, and Elsa learn from Sven that Olaf has gotten lost in the woods and is being chased by hungry wolves. When they find the snowman, Olaf reveals that he had been on a mission to find holiday traditions for Elsa and Anna. This kicks off a party in the woods, attended by all of Arendelle.
- Kai is named after one of the protagonists of the original Snow Queen tale by Hans Christian Andersen, by which Frozen was inspired. In the original story, Kai (or Kay) was the imperiled best friend (brother in some interpretations) of Gerda, a brave heroine determined to rescue him from the Snow Queen.