Mossan, whose full name is Man Motoyama, is a seventeen-year-old high school student and one of the closest friends of the protagonist Kana Koumoto in FLCL Alternative. She is part of a tight-knit group that also includes Hijiri and Pets, and the four of them spend most of their free time together, navigating the ordinary challenges of adolescence. Mossan is widely regarded as the most motivated and hardest working member of the group. She has a clear and ambitious dream of becoming a fashion designer, and she has already taken concrete steps toward that goal by qualifying for a design contest. Unlike some of her friends who are uncertain about their futures, Mossan has a strong sense of direction and is willing to put in the effort to achieve her aspirations.

Her motivation is deeply rooted in her personal values. She comes from a family that struggles financially, and she takes on a part-time job as a safety guide at a construction site in order to earn money for fashion design school tuition. She is determined to achieve her dream on her own terms, and she initially becomes upset when her friends try to help by taking construction jobs to support her. She feels that the dream will not be worth anything if she does not earn it herself, which reveals a strong sense of independence and pride in her own abilities. However, she eventually allows Kana to assist her with the design contest, showing that she is capable of accepting help when it is offered in a way that respects her autonomy. She does not win the contest, but she takes pride in her work and declares that she will become the world's next top model, indicating resilience and self-confidence.

In the story, Mossan serves as an anchor of responsibility and purpose within the friend group. She is the one who first suggests building a bottle rocket out of discarded Dr. Pepper bottles, which sets the early events of the series in motion. Her role becomes central in the episode focused on her character, where her overwork and stress lead to a physical collapse, prompting her friends to rally around her. This episode highlights her external struggle: she is talented and hardworking, but her family's financial situation makes it difficult for her to pursue her passion without sacrificing her health. Her development involves learning to balance her drive with the support of her friends and to take pride in her work regardless of the outcome.

Mossan's key relationships are with Kana, Hijiri, and Pets. She is a loyal and supportive friend, though she is also the one who is most focused on her own goals. Her bond with Kana is especially significant, as Kana helps her prepare for the contest and encourages her when she is feeling overwhelmed. Mossan also has a close relationship with her mother, who is aware of her hard work and shares her concern. In terms of notable abilities, Mossan possesses a clear talent for fashion design, as demonstrated by her qualification for a design contest and the dress she creates. She also has a strong work ethic and the ability to motivate others, as seen when she convinces her friends to build the bottle rocket. She does not have any supernatural powers; her strengths are her determination, responsibility, and creative skill.