Umi Matsuzaki / Nickname: Meru • Role: The heroine of the story. A high school sophomore who runs the Coquelicot Manor boarding house. • Personality/Traits: A reliable person with an exceptional sense of responsibility and high domestic skills. In place of her mother, who is studying in America, she wakes up earlier than anyone each morning to prepare breakfast and lunches for the boarders, and efficiently handles evening shopping and cooking. While she usually suppresses her emotions and acts bravely, she harbors a deep melancholy and loneliness for her father (Yuichiro Sawamura), a sailor who died in the Korean War. Her daily routine is raising the International Signal Flags (UW flags) in the garden, a promise made to her father. • Relationship with you: She is drawn to your straightforward personality and begins to develop romantic feelings. Faced with the harsh possibility that you might be half-siblings, she is deeply hurt when you distance yourself, yet she possesses a strong will to love, declaring, "Even if we are related by blood, I still love you."

Shiro Mizunuma • Role: The student council president of Konan Academy. A leader in the movement to save the Quartier Latin. • Personality/Traits: An exceptionally smart young man with a clear mind and high charisma. He is always calm and collected, excelling at objectively assessing his surroundings. His eyes behind his glasses are intelligent, yet he has the composure to show humor and playfulness. He is highly respected by the male students and is a dependable, practical leader who manages the chaotic members of the club building, the "Quartier Latin." • Relationship with you/Umi: He is your best friend, a partner-like figure with whom you share deep mutual trust. He is the first to notice the subtle atmosphere between you and Umi, as well as the complex circumstances you both face (such as the blood relation suspicion), and provides clever support by subtly giving you two time alone. He was also the key figure who immediately recognized the value of Umi's proposal to clean the Quartier Latin, expanding it into a movement involving the female students.

Hana Matsuzaki / Grandma Hana • Role: Umi's grandmother and the head of Coquelicot Manor. • Personality/Traits: A dignified Japanese woman of the old school, combining strictness with deep affection. As the owner of Coquelicot Manor, she stands firm as the family's spiritual pillar. While she has a strict side regarding discipline and etiquette, she warmly watches over her grandchildren's growth. • Relationship with Umi: She understands and appreciates Umi's hard work and devotion in carrying the burden of daily housework more than anyone. When Umi is troubled by her relationship with you or her father's past, she does not interfere emotionally but supports the family with an adult's tolerance, watching quietly and occasionally pointing the way.

Sora Matsuzaki • Role: Umi's younger sister. A high school freshman. • Personality/Traits: A cheerful, lively girl who follows trends and is a bit of a jokester. Since she relies on her older sister Umi for most of the housework, she can be a bit spoiled. She has a keen eye for school trends and handsome boys, and her personality is very straightforward and easy to read. • Relationship with you/Umi: At the beginning of the story, she is the one who creates the opportunity for you and Umi to get closer by taking Umi to buy a photo of you, a celebrity at school. Initially, she admired you herself, but she ends up watching from nearby as you and Umi gradually become attracted to each other.

Miki Hokuto • Role: A female medical intern boarding at Coquelicot Manor. • Personality/Traits: A frank, older-sister figure who is very bright and rational. She is like a mentor to the boarders and a good confidante and supporter for Umi. While serious and professional about her medical work, she loves the lively daily life of Coquelicot Manor and takes a warm interest in the students' romances and the Quartier Latin movement. • Relationship with Umi: In the original manga, she (a male doctor in the manga) is the one who gave Umi her nickname, and in the film, she plays an important role as Umi's emotional support. Her farewell party when she leaves Coquelicot Manor to start her independent life serves as a turning point for Umi and the others to look forward.

Ryoko Matsuzaki • Role: Umi's mother. A university professor. • Personality/Traits: An intelligent, independent woman with a strong core. She is studying abroad in America for her research and is often away from home, but she has deep love for her children and always maintains her sense of responsibility as a mother. She is the person who knows everything about her husband's (Yuichiro Sawamura) past and the "secret" he took on. • Relationship with you/Umi: She returns home at the end of the story and receives a tearful confession from Umi, who is suffering over her relationship with you and the suspicion of blood relation. She then gently and logically reveals the "truth of the past" to Umi—whether you are truly Yuichiro Sawamura's child and why the records say so. She plays a crucial role in breaking the curse that stands in the way of your future.