On July 7, Yagi was announced as one of the winners of the Hello! Project "Juice=Juice" "Tsubaki Factory" Goudou Shin Member Audition audition and would join Tsubaki Factory alongside Kasai Yuumi, Fukuda Marine, and Yofu Runo.
She has a pet named Mapuru.
As of April 2021, Yagi is currently in her last year of high school.
Here is a list of nicknames that was used to refer to Yagi Shiori:
- Yagi-chan (八木ちゃん)
- Shiori (しおり)
- Name: Yagi Shiori (八木栞)
- Nicknames: Yagi-chan (八木ちゃん), Shiori (しおり)
- Birthdate: September 19, 2003
- Birthplace: Aichi, Japan
- Blood Type: O
- Western Zodiac: Virgo
- Eastern Zodiac: Goat
- Hello! Project Status:
- 2021-07-07: Tsubaki Factory member
- UP-FRONT PROMOTION Status:
- 2021-07-07: Member
- Tsubaki Factory Member Color: Orange
- Hello! Project Groups:
- Tsubaki Factory (2021-present)
- [2021-] Hello! Project Station
-  Cinderella (as Cinderella)
-  Kaguya Hime (as Yuki)
- She has the same birthday as former Hello Pro Korea Kenshuusei member Jang Dayeon.
- She shares the same last name as Lovelys member Yagi Saki.
- Her favorite Hello Pro Kenshuusei trainee was Yofu Runo. She is happy to be together in the same generation as her.
- She wants to improve her performance and expressions to match the rest of the group, and that she wants to become a member who is able to lead the way for the rest of Hello! Project.
- She has learned ballet and jazz dance.
- She admires Kishimoto Yumeno for her singing and personality gap.
- Her audition number was 128.
- Her favorite Shiki Theatre Company production is "Yume Kara Sameta Yume".
- She loves Filipino food.
- Gallery:Yagi Shiori
- List:Yagi Shiori Discography Featured In
- List:Yagi Shiori Concert & Event Appearances
- List:Yagi Shiori Publications Featured In
- List:Yagi Shiori Pocket Morning Weekly Q&A