All links lead to more information. Lots more, in most cases.

$$ Seiyuu: Most people know him as a seiyuu, or a voice actor (mainly for anime). More info within.

$$ Musician: Like many other seiyuu, Koyasu sings. Unlike many other seiyuu, he's actually good at it! :O (S'okay, Souichirou, we still love you)

I don't think he's been anything else, but if I'm wrong you can contact me about it. Note: Odd jobs don't count.