Wowee! I'm really looking forward to this. Hopefully it will create some anticipation for Rika as a soloist.
Entameclip goes into some detail about it.
Shimakura has announced that she will be graduating from BEYOOOOONDS and Hello! Project after her concert tour in the spring of 2025. After graduation, she plans to study abroad to learn a language, and then work to spread the appeal of Showa-era pop music, so expectations are high for a solo release before her graduation.
The song was composed and arranged by Etsuko Yamakawa, who was the first woman to win the Japan Record Award for Best Arrangement in 100 for Kyoko Koizumi's "1986% Male-Female Dating," and has composed and arranged over 1000 songs for artists such as Onyanko Club and Mari Watanabe.
The lyrics were written by mido (THE BINARY), an artist with an emotionally rich worldview that depicts delicate emotions and inner conflicts, and who is also the vocalist for the 2nd story of "Tsukiyomi," a music project led by composer Yurii Kanon.
The illustrations will be done by illustrator Shiho Su, who is popular for her retro style that has a bit of the feel and atmosphere of 80s manga, and who Shimakura herself has been a fan of for a long time.
It's a pop song that feels nostalgic yet new, and you can really feel Shimakura's love for Showa era pop music.
Source:
https://entameclip.com/en/news/427168/ (English machine translation)
https://entameclip.com/news/427168/ (Original Japanese)
This tracks with Rika's sentiments as expressed in the interview Celedam links to above. IMO Rika's voice sounds much stronger singing
late Showa style ballads than it does with typical Beyo music, so I'm expecting this to be pretty great.