I found some footage of some online Japanese Dreamcast games on the Japanese video sharing site, Nico Video, back in 2017. I cleaned them up a tiny bit (a bit of sharpening and deinterlacing) and reuploaded it to YouTube. I didn't think online gameplay of these games existed until now! Very cool to see!
Sega Rally 2 from 1999?
Guru Guru Onsen from 1999 or 2000?:
Sega Tetris from 2001:
Capcom vs. SNK Millennium Fight 2000 Pro from 2000?:
Virtual-On: Oratorio Tangram from 1999/2000?: