Danbooru can’t normalize Twitter image links since the URLs don’t indicate which account posted it. It needs to be manually replaced with the tweet URL, which has been done for you here.
According to the third-party source (a geocities.ws fansite), this is Laguna, though this webmaster misidentifies the characters in some of the other pictures they host. The hair looks similar so I'm going to agree that this is probably Laguna as a dragon, but I don't know for sure and wasn't able to find it on the rendezvous's original site on the Wayback (it's very incomplete).
On the plus side, the images that are both in this gallery and the artist's original site have the same MD5s, so this is probably a good source for uploads. The images are not compressed, just low res, because they originate from the very early 2000s.
This was drawn by Daoko, the singer of "ME!ME!ME!" and "Uchiage Hanabi". She posted this after an episode of Suisei's radio show aired in which she appeared and talked about how much she liked VTubers, especially Miko.
