Aine Yuuki, a regular student at Star Harmony Academy, meets Mio Minato from the idol division. When Mio learns of Aine's desire to make friends, she encourages her to explore the world of Aikatsu. Aine becomes friends with Maika Chōno and Ema Hinata, fellow idols on the same journey. As Aine and Mio's bond strengthens, they become "Diamond Friends," determined to shine brighter than ever. Karen Kamishiro and Mirai Asuku, respected members of the Diamond Class, join Aine and Mio on their journey.