TV-Series
Description
Marimo Hatanaka is a fourth-grade student in the Star Class at Seiyo Academy who appears as a supporting character during the school's choral competition arc. She is a talented pianist who auditions and is selected to provide the piano accompaniment for the Seiyo Academy chorus. Her most defining trait is her dedication to music and her aspiration to continue playing the piano as she grows older. Marimo is portrayed as a kind and gentle girl who readily offers help to others, demonstrated when she notices that classmate Seiichiro Suzuki struggles with singing and volunteers to practice with him, playing the piano so he can improve.

Despite her skill and good nature, Marimo is sensitive to criticism. During a rehearsal for the competition, she makes a simple mistake on the piano, and Saaya Yamabuki and her group harshly criticize her for the error. Deeply upset by the harsh words, Marimo apologizes and flees the practice room. The incident causes her heart's egg to transform into an X Egg, which then hatches into an X Character, a corrupted version of her would-be self. This event triggers the central conflict of the episode: the Guardians must find and help Marimo before the competition. With the unintentional help of Seiichiro, who genuinely cares about her well-being, Amu Hinamori is able to transform into Amulet Heart and purify the X Character, restoring Marimo's confidence.

Marimo possesses a Guardian Character of her own, which appears in the story as a small figure with blonde hair and a pink eighth note on the left side of her hair. This Guardian Character reflects her musical passion and gentle nature. In terms of relationships, her most significant bond within the episode is with Seiichiro Suzuki, as she takes on a supportive, almost mentoring role in helping him prepare for the competition. She also interacts briefly with the principal Guardians, particularly Tadase Hotori, who checks on her after her distress. Marimo's development is centered on learning to face criticism and regaining her self-assurance through the support of her friends. Her notable ability is her skill as a pianist, which serves as the foundation of her role in the story and her connection to her dreams and aspirations.