This is an awesome original animation promotional video for the manga series「セガのゲームは世界いちぃぃぃ!」by anime and manga artist TAKAHIRO YOSHIMATSU (吉松 孝博). The video was released in a supplementary GD-ROM of the DREAMCAST magazine「DRIMAGA」.
The manga series became a hit thanks to the main character「CASKO-SAN」, who is portrayed as a Japanese teenage girl on a sailor suit with a DREAMCAST console for a head. CASKO-SAN became pretty much the iconic character that ended up representing the DREAMCAST fan support in Japan.
This was the only anime promo video ever done for the series, and it is an excellent animation video, so I really recommend you watching it.