Nao Umiyama is a supporting character in 365 Days to the Wedding. She is the childhood friend of Takuya Ohara, having grown up living next door to him in their shared hometown. After three years of working as a glass craftswoman, she moves into the same apartment building as Rika Honjoji in order to be closer to her workspace. Nao is outspoken, lively, and approachable, with a straightforward and cheerful demeanor that quickly draws Rika out of her shell. Her easygoing personality and genuine warmth spark an unlikely yet strong friendship between the two women, and she becomes a trusted confidante. Though she initially discovers that Takuya and Rika's engagement is a fake arrangement, she does not act as a rival or antagonist. Instead, she chooses to support the couple wholeheartedly, offering encouragement and practical advice as their relationship evolves. Her role in the story is to provide an external perspective on the central fake-relationship plot, helping both protagonists navigate their feelings and deepen their bond. Nao's background as a glass artisan is a notable aspect of her character; she works at a glassblowing studio and has a clear passion for her craft, which she speaks about with pride. Her development involves transitioning from a childhood friend who teases Takuya to a key ally who helps him and Rika grow closer. Her ability to read people's emotions and her honest communication style make her an effective mediator and a stabilizing presence in the group.