co-star; co-performer
Refers to someone who performs together with another person in a show, film, play, or other performance.
He became a co-star with a famous actor in the new movie.
On stage, I was perfectly in sync with my co-performer.
Compound of 共 (きょう, 'together') + 演 (えん, 'perform') + 者 (しゃ, 'person').