He is best known for scripting the television series Iron Chef and the 2009 Academy Award for Best Foreign Language Film recipient Departures.
He has a brother named Shōdō (将堂)[1] three years younger than him who has Down syndrome; Koyama says their parents strove to raise them equally.
[1] Continuing this screenwriting after graduation, Koyama began getting attention for his work on Fuji Television's Kanossa no Kutsujoku (1990–1991), a late-night show which "took various modern-day social phenomena and products and explained them satirically by presenting them as historical events and folklore".
[4] Koyama dropped many of the book's religious themes, changing them with more humanistic ones,[5] and integrated a subplot from a novel he was writing.
[6] For the title he coined the term okuribito, a euphemism for morticians derived from the words okuru ("to send off") and hito ("person").
[3][16] He is the representative of N35 Inc., a literary agency specializing in broadcast screenplay writers,[16] and he is president and CEO of the marketing firm Orange and Partners.