Mitsuki Kouyama, who performs under the stage name Full Moon, is the main protagonist of the anime Looking for the Full Moon. She is a twelve-year-old girl with a terminal malignant tumor in her throat, known as a sarcoma, that restricts her breathing and singing ability. She was raised in an orphanage before moving in with her strict grandmother, Fuzuki, who forbids her from pursuing music. During her time at the orphanage, Mitsuki formed a deep bond with a boy named Eichi Sakurai, who was several years older. When Eichi was adopted and moved to America, the two made a promise: he would become an astronomer, and she would become a professional singer. Two years later, two shinigami – Takuto Kira and Meroko Yui – appear before Mitsuki and inform her that she has only one year left to live. Determined to fulfill her dream, Mitsuki persuades Takuto to help her. He gives her a pill that transforms her into a healthy, sixteen-year-old version of herself, allowing her to audition for a record label. She passes the audition under the stage name Full Moon and signs with Seed Records, embarking on a singing career while hiding her true age and illness.

Mitsuki’s personality is cheerful, innocent, and remarkably resilient. She approaches life with optimism and a strong sense of determination, even as her health deteriorates. She states that she fears losing her voice more than dying, which underscores her deep, genuine love for music. She is kind-hearted and empathetic, often thinking of others’ feelings before her own. Her primary motivation is initially tied to her promise to Eichi – she wants to become a singer so that he will hear her songs and remember her. Over time, however, her motivation deepens as she discovers her own passion for singing and forms new attachments, particularly with Takuto.

In the story, Mitsuki serves as the central figure whose journey connects the human world with the supernatural realm of the shinigami. Her transformation into Full Moon allows her to achieve fame and grapple with themes of mortality, love, and the pursuit of dreams. Her key relationships include Eichi Sakurai, her first love whose memory drives her early actions; Takuto Kira, the shinigami who becomes her mentor and eventually her romantic interest; Meroko Yui, a fellow shinigami who befriends and supports her; and her grandmother Fuzuki, whose initial opposition gradually gives way to concern and love. Mitsuki also interacts with other shinigami, including Izumi Rio, and learns the truth about Eichi’s death – he died shortly after moving to America. This revelation forces her to confront grief and ultimately to let go, allowing her to open her heart to new feelings for Takuto.

Mitsuki undergoes significant development throughout the series. She begins as a shy, sickly girl who is afraid to defy her grandmother, but she grows into a confident performer who stands up for her dreams. She learns to accept the inevitability of death without giving up on living fully. Her emotional maturity is reflected in her decision to undergo surgery to remove the tumor, even at the risk of losing her voice, and later to retire from the stage. By the end of the story, four years after her final concert as Full Moon, she has resumed singing under her own name and reunites with Takuto, who has awakened from a coma. Mitsuki’s arc shifts from singing for Eichi to singing for herself and for the people who love her, culminating in a new beginning.

Mitsuki’s most notable ability is her extraordinary singing voice, which can convey deep emotion and affect everyone who hears it. Even with her illness, her voice possesses a unique power that moves audiences and touches hearts. With Takuto’s magical assistance, she temporarily transforms into a healthy, older version of herself, enabling her to perform professionally. This transformation is not a permanent ability but a gift that allows her to chase her dream within her limited time. Her voice and her music remain her defining traits, serving as both her legacy and her means of connection with others.