Mitsuko Umenoki is a supporting character in Tying the Knot With an Amagami Sister. She is a high school student who shares a class with Uryuu Kamihate and the Amagami sisters. She serves as the class representative and is best friends with Yuna Amagami, often seen in her company. Mitsuko comes from a family that runs a long-established dango or dumpling shop that has been operating for over a century. In earlier times the shop was quite popular and even had multiple branches, though business has slowed in the present. Her distinctive hairstyle, which consists of light-colored hair tied into a high bun with square bangs and chin-length strands on either side, is often noted for resembling two round dumplings. Because of this, she is affectionately called Omitchan by those around her. She has a kind and bubbly personality, and she speaks with a warm Kansai dialect. Her role in the story is primarily as a supportive friend and classmate, providing a cheerful presence and helping to ground the main cast. Beyond her close friendship with Yuna, she does not have a deep personal arc or notable supernatural abilities, and her character remains largely unchanged throughout the series.