Mitsuki Kouyama is the twelve-year-old protagonist of the anime Looking for the Full Moon. She was born to Aoi Koga and Hazuki Kouyama, though her mother died shortly after giving birth and her father died when she was a young child. After her parents’ deaths, she lived in an orphanage before being taken in by her strict grandmother, Fuzuki Kouyama, who forbids her from pursuing music. It was in the orphanage that Mitsuki met and fell in love with Eichi Sakurai, an older boy who dreamed of becoming an astronomer. Before he was adopted and moved to America, they made a promise to each other: Mitsuki would become a professional singer and Eichi would become an astronomer, believing that achieving their dreams would bring them back together. Years later, Mitsuki still carries this promise as her deepest motivation.

Mitsuki suffers from a malignant tumor in her throat, a sarcoma that makes breathing difficult and singing painful. She refuses surgery to remove it because the operation risks permanently damaging her vocal cords, which would end her chance of ever singing professionally. Her grandmother insists on the surgery and dismisses Mitsuki’s musical ambitions, leaving her feeling trapped. Her situation becomes even more dire when two shinigami, Takuto Kira and Meroko Yui, appear and reveal that she has only one year left to live. Rather than surrendering to despair, Mitsuki sees this as a reason to act immediately. She strikes a deal with Takuto: if he helps her become a singer, she will willingly give up her soul when the year is over. Takuto gives her the ability to temporarily transform into a healthy sixteen-year-old girl, allowing her to audition and perform without the limitations of her illness. Under the stage name Full Moon, she launches a successful singing career and quickly rises in the music industry.

Mitsuki is characterized by her optimism, determination, and gentle kindness. Even in the face of a terminal illness, she maintains a hopeful outlook and a strong will to pursue her dream. She is not naive about her condition or the dangers she faces, but she chooses to focus on what she can do rather than what she cannot. Her love for singing is profound, and she often turns to music as a way to express her emotions and find strength during difficult moments. She is also deeply caring toward the people around her, showing compassion and empathy even when her own situation is dire. Her primary ability is her extraordinary singing voice, which allows her to convey deep emotion and connect powerfully with audiences. Her talent is so compelling that it moves judges, fans, and even the shinigami assigned to collect her soul.

Her relationships are central to her journey. Her first love, Eichi Sakurai, serves as her initial motivation, and she believes that becoming a famous singer is the way to reunite with him. Her relationship with Takuto evolves from a transactional arrangement into a deep emotional bond. Takuto, initially detached and reluctant, becomes her mentor and protector, and over time they develop mutual feelings. Meroko, the other shinigami, becomes a close friend and ally. Mitsuki’s grandmother, though strict and disapproving of her musical ambitions, ultimately cares for her and represents the familial ties that Mitsuki must navigate as she pursues her dreams.

Mitsuki undergoes significant development throughout the story. She begins as a girl driven by a childhood promise and the hope of reuniting with Eichi, but she gradually learns to face the truth about her circumstances. She discovers that Eichi died shortly after leaving the orphanage, a truth she had kept hidden out of regret and grief. With Takuto’s help, she comes to terms with his death and realizes that her singing has value beyond her original promise. She also learns the truth about the shinigami, that they are the spirits of humans who died by suicide, and that Takuto himself was a singer who lost his voice and attempted suicide. This deepens her understanding of life, death, and the importance of living fully. Eventually, she chooses to undergo the surgery to remove her tumor, accepting the risk of losing her voice, and decides to return home. In the final resolution, after a confrontation with the shinigami authorities, she survives and retires as Full Moon. Four years later, she resumes her singing career under her real name and reunites with Takuto, who has recovered from a coma and regained his ability to sing. Her story is one of resilience, self-discovery, and the courage to pursue one’s dreams despite overwhelming odds.