Dreamcast bios font page has been updated with some Javascript to help you make use of the characters you need.
On a compatible browser, move the mouse over the tables to find the byte offset for the character.
Also for the JIS X0208 characters you can get the double-byte values for various encodings.
The SEGA Dreamcast has an extensive font stored in the bios.
Whilst most people will use a texture to produce a pretty font of their own choosing, there are some occasions when you might want to make use of the inbuilt font information. Here is a reference page to help you find the characters you need.