Lotte was born in a family of witches in Finland, her family owns a magic item shop passed down for generations. During her childhood, the other children made fun of her for coming from a family of witches, however, she found a consolation in reading the Night Fall novels. Her grandmother taught her a special song that can call spirits and appease them, which Lotte used to have the spirits form a rainbow for her.
She decides to go to Luna Nova Academy to acquire a license of magic tools and thus be able to inherit her family shop.
Lotte is Akko's friend, often worried about her antics. She aids Akko in the dungeon and against the ancient dragon, being injured in the process.
Lotte becomes embroiled in Akko's plans for the town's parade, reluctantly becoming project manager. She expresses her concerns about the project's scope to Akko, who is too engaged in her fantasies to listen. Akko's impulsiveness accidentally causes her and Lotte to rip a treasured piece of sheet music belonging to Lotte's ancestors. This is the final straw and she kicks Akko out of the room. Next morning, Lotte bluntly tells Akko the project will fail and wants to do something separate for the parade, abandoning her. Later, Lotte witnesses Akko's hard work in the library for the parade.
During the parade, Lotte arrives just in time to save Akko and Sucy from being devoured by the awakened Titan's angry spirits with her ancestor's ancient song. She sings and pacifies all of them before giving Akko a gift: a hand-made Shiny Chariot hat. Akko tearfully apologizes for her selfishness while Lotte accepts and expresses her admiration for Akko's passion. She then forms the Shiny Ballista with Akko and Sucy and pacifies a rampaging Titan.