Mia Taylor, from New York.
She's a third-year, but because she skipped grades, is actually only 14, the youngest idol in the cast. Daughter of the "famous Taylor musical family", which I guess we're supposed to take as that she's James Taylor's granddaughter? Has written hit songs for others, and her arc thus far is learning to write and perform for herself. Appeared in the game when Lanzhu showed up, and was, like her, initially antagonistic; over the course of the game's second season storyline, she softened and really got attached to Rina. She and Lanzhu have recently joined the Nijigasaki High School Idol Club.
(She was in the most recent game event, being fussed over by Hanamaru, and they really had a great doting-big-sister/tsundere-little-sister thing going.)