She is classically trained on the 21-string, 17-string, 18-string, and 13-string kotos as well as on shamisen; when called upon, she employs her voice and electronics in performances and on recordings. Her collaborators have included Elliott Sharp, Peter Brötzmann, Paal Nilssen-Love, Otomo Yoshide, Cassiber, and dozens more.

Born in Tokoname, Aichi prefecture, she began studying Japanese traditional music on the koto under Satomi Kurauchi at age six. Two years after graduating from Aichi Junior College in 1983, she was admitted to the Sawai Koto School in its advanced studies program. There she studied koto and shamisen with masters Tadao Sawai and Kazue Sawai, and explored contemporary music for the first time. She also enrolled in National Broadcasting Network's (NHK) one-year koto performance course, graduating in 1986 and making her debut in the Japanese Cultural Event at the Tokyo Summit. Graduating from Sawai Koto School in 1987 with Master's degrees in performance and teaching, she won a Japan Foundation Grant and participated in a 12-concert tour in Southeast Asia, Germany, Italy, and England. Her first appearance on a recording was on the Sawai Koto Ensemble's Koto.

In 1989, she was a guest professor of Japanese traditional music and koto at Wesleyan University in the U.S. While there, she delivered her first performance (of many) at New York's Bang on a Can Festival. In 1992, she made her debut at the Blue Note jazz club. From 1993 to 2016, she contributed to recordings by artists and ensembles including Kazue Sawai Koto Ensemble, Tetsu Saitoh, Yoshide, and as a full member of member of the recording bands Kokoo, Hoahio, and Koto Vortex. In 1999, she released Shizuku, her solo debut on Tzadik. She followed it with Seventeen on Zip in 2005.

She began her long association with the Idiolect label in 2006 as a co-leader on the trio date Live at SuperDeluxe with Nilssen-Love and bassist Ingebrigt Håker Flaten. Two years later, again with Brötzmann and Nilssen-Love, she issued Head On, followed by Volda with the same players, and Reflexions with Sharp. Yagi remained in demand as a session player and touring soloist: In 2012, she was also a featured soloist on Akira Sakata & Chikamorachi's Flying Chikamorachi. In collaboration with Tamaya Honda, she released Dojo, Vol. 1 on Idiolect. A year later, Yagi, Lasse Marhaug, and Nilssen-Love released Angular Mass, followed in 2016 by Soul Stream, which added Joe McPhee to the ensemble. Both recordings were issued by PNL. ~ Thom Jurek