Tomokazu Seki
In the late 1990s, Koyasu worked on conceptualizing for the media franchise "Weiß Kreuz". He also formed the voice acting unit "Weiß" consisting of voice castmates Shin-ichiro Miki, Tomokazu Seki and Hiro Yūki, and became the first male voice actor to appear on the cover of a voice acting magazine and the first voice actor to make a music clip. In 2000–2001, he was active in music under the name ZAZEL.