Keita Amemiya has worked across both animation and live-action, often handling multiple roles on his projects. His live-action work includes directing Kamen Rider ZO and Mechanical Violator Hakaider, as well as supervising Shin Kamen Rider. He served as director of photography on Kamen Rider J.

In animation, Amemiya created and directed G-9 and served as original creator on Tweeny Witches (TV series) and Mahō Shōjo Tai Arusu: The Adventure. He contributed the original concept and visual setting for Iria - Zeiram the Animation.

The Zeiram films represent some of his most notable work—he directed, wrote, and handled character design for both the original Zeiram live-action movie and its sequel Zeiram 2, also serving as original creator on the second film.