Eiko Tanaka is the chief executive officer and president of Studio 4C, which she founded in 1986. She is also the chief executive officer of a production company called Beyond C.

Studio 4C has produced such anime as Memories, Tobira o Akete, Debutante Detective Corps, Eternal Family, Noiseman Sound Insect, Spriggan, Uraroji Diamond, Piroppo, Princess Arete, The Animatrix (as a joint production with with Warner Bros.), Hijikata Toshizo: Shiro no Kiseki, Kimagure Robot, Mind Game, Super Robot Monkey Team Hyperforce Go!, Tweeny Witches, Steamboy, Tekkonkinkreet, Ani*Kuri15, Genius Party, Detroit Metal City, First Squad – The Moment of Truth, and two shorts for Halo Legends.

In addition to these anime productions, Studio 4C has also produced some music videos. These include "Extra" by Ken Ishii, "Four Day Weekend" by The Bluetones, "Survival" by Glay, "Connected" by Ayumi Hamasaki, "Pervyi Otryad" by Ligalize, and "Passion" by Hikaru Utada. The company has also produced some short films. In the 2000s, the company also branched out to do some work for video games and commercials.

Tanaka herself has credits in anime as an executive producer, a producer, an animation director, a production manager, and as a production chief. Tanaka had her first anime credits in the 1980s, when she served as a producer on Manga Aesop Monogatari in 1983, a production chief on Studio Ghibli's My Neighbor Totoro in 1988, and as a production manager for Studio Ghibli's Kiki's Delivery Service in 1989.

During the 1990s, Tanaka kept herself busy as an executive producer, a producer, and as a production manager. As an executive producer, she worked on 1997's Eternal Family. As a producer, Tanaka worked on Noiseman Sound Insect in 1997, Spriggan in 1998, and Survival 2.7D in 1999. In 1995, she served as a production manager on Tobira o Akete.

The 2000s have definitely been Tanaka's most prolific decade for anime credits. She served as an executive producer on Table and Fishman in 2002, Hijikata Toshizo: Shiro no Kiseki and Tweeny Witches in 2004, Tekkonkinkreet in 2006, and Detroit Metal City in 2008. As a producer, Tanaka worked on Beyond in 2000, Princess Arete in 2001, End of the World in 2002, The Animatrix in 2003, Mind Game in 2004, First Squad – The Moment of Truth in 2009, and the "Origins" and "The Babysitter" shorts for Halo Legends in 2010. She also served as an animation director on Tweeny Witches: The Adventures in 2007.