Yagi Shiori was born on September 19, 2003 in Aichi, Japan.
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 Maltipoo named Mickey (ミッキー). She calls him Mickey-kun (ミッキーくん).
The following list are notable friendships Yagi Shiori has acquired:
She graduated from high school in March 2022.
Here is a list of nicknames that was used to refer to Yagi Shiori:
- YagiShio (やぎしお): Used by Tsubaki Factory members.
- YagiShii (やぎしー): Used by Tsubaki Factory members. Alternate spelling: やぎシー, used by Yofu Runo.
- Shiori (しおり)
- Yagi-chan (八木ちゃん)
- Name: Yagi Shiori (八木栞)
- Nicknames: Yagi-chan (八木ちゃん), Shiori (しおり), YagiShio (やぎしお), YagiShii (やぎしー)
- 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:
- Hello! Project Groups:
- Tsubaki Factory (2021-present)
- [2021–] Ikuze! Tsubaki Factory (行くぜ！つばきファクトリー)
-  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.
- She has been to Negros, Philippines in summer of 2019 as a tourist.
- She has a signature pose, the "goat (Yagi) pose".
- She loves to post her home-cooked meals on her blog. Fans refer to it as 'Yagi meshi' (八木メシ), where 'meshi' means 'meal'.