This is the love letter you're looking for. It's titled ラブレター and this cover song was performed by the star highlights of this installment; Uzuki Shimamura (CV: Ayaka Ohashi), Miho Kohinata (CV: Minami Tsuda), and Kyoko Igarashi (CV: Atsumi Tanezaki). Once you listened to it, it's worth more than you've experienced it from Debut to the now mega difficult Master+ difficulty setting.
Apart from that, you can expect two new songs as well such as メルヘン∞メタモルフォーゼ! by Nana Abe (CV: Marie Miyake) and 薄紅 by Sae Kobayakawa (CV: Rika Tachibana).
Be sure to keep playing Starlight Stage and watch out for more on this range!
1) ラブレター (M@STER VERSION)
4) ラブレター (M@STER VERSION) オリジナル・カラオケ
5) メルヘン∞メタモルフォーゼ! オリジナル・カラオケ
6) 薄紅 オリジナル・カラオケ
7) ラブレター (GAME VERSION)