
Sei Ashina was born Igarashi Aya, and assumed the stage name Sei Ashina. Prior to her acting career, Ashina was a model. She made her acting debut in the 2002 TBS Television series The Tail of Happiness (しあわせのシッポ), modeling that year in magazines including Shogakukan's CanCam and Shueisha's Pinky, and was best known for starring as Hime in Kamen Rider Hibiki. She was also known for her role as The Girl, an unnamed concubine, in Silk (2007).

Saru Lock: The Movie
2010 · as Ritsuko Mizuhara

Silk
2007 · as The Girl

Kamen Rider Hibiki The Movie: Hibiki & The Seven War Oni
2005 · as Hime

Kamui
2009 · as Mikumo

KING GAME
2010 · as Chekov

Killing for the Prosecution
2018 · as Driver

Impossibility Defense
2018 · as Risa Yumehara

Perfect World
2018 · as Aoi Nagasawa

AI Amok
2020 · as Maika Hayashibara

The Tale of Genji: A Thousand Year Enigma
2011 · as Yugao

ST: Aka to Shiro no Sôsa File the Movie
2015 · as Midori Yuki

Elevator Trap
2009

Kamogawa Horumo: Battle League in Kyoto
2009 · as Kyoko Sawara

The Last Revenge
2011

Cat Taxi
2010

Hard Romanticker
2011 · as Natsuko

Kamen Rider Hibiki: Asumu Transform! You can be an Oni, too!!
2005 · as Super Hime

Kaidan Horror Classics
2010