Mayuko Satou is a supporting character in the anime Just Because!. She is a third-year high school student and one of Mio Natsume’s closest friends. She has short hair and wears glasses, giving her a studious and slightly dorky appearance. Her hair is blonde and her eyes are yellow. Mayuko is deeply loyal to Mio and becomes fiercely protective when she believes Mio’s feelings might be hurt. Because Mio has long harbored romantic feelings for Haruto Souma, Mayuko initially displays strong hostility toward Hazuki Morikawa, whom she sees as a potential rival who could take Haruto away from Mio. This protective instinct defines much of her early role in the story. Mayuko is described as a coquettish teenager who cares about her appearance and values her friendships above all else. Her primary motivation is to safeguard Mio’s happiness, and she often acts as a satellite character who influences the group’s romantic dynamics by vocalizing her concerns. Over the course of the series, she remains a steadfast presence within the friend circle that includes Mio, Eita Izumi, Haruto, and Hazuki. While she does not possess any extraordinary abilities, her unwavering loyalty and willingness to speak her mind make her a notable figure in the social web of the story. Her development is subtle, centering on her gradual acceptance of the evolving relationships around her.