Here's how I change the font using the recipe. I'll let you figure out how to change to your font.
Code:
extra_css = '@font-face {font-family: "serif1";src:url(res:///Data/FONT/angsau.ttf)} @font-face {font-family: "sans1";src:url(res:///opt/sony/ebook/FONT/tt0003m_.ttf)} body{font-family: serif1, serif} .article_description{font-family: sans1, sans-serif}'
How I wish I could read japanese...*sigh*