Student Aine Yuuki attends the standard section of Star Harmony Academy, where she encounters idol Mio Minato. The enthusiastic idol invites Aine to join Aikatsu, helping her achieve her desire for companionship. Together they meet fellow performers Maika Chōno and Ema Hinata, forming new bonds. Aine and Mio become inseparable companions, earning the title of luminous "Diamond Friends." Likewise, Karen Kamishiro and Mirai Asuku are designated as "Diamond Friends" and occupy seats in the bright Diamond Class.
