Found this mashup of a whole bunch of songs. Apparently it uses Kaito's Append Voicebank from around the time VOCALOID got shifted from V2 to V3, causing the append to only ever be available in some demos. I guess it was never commericially sold and is considered lost, however I checked the Lost Media Wiki and one of the administrators posted back in 2017 that it wasn't notable enough to have its own page dedicated to it.
On another note, I can't seem to download the video. I typically download NIcoNico videos by opening Inspect and spotting and downloading the mp4 file from there, however on this video everything is in some format called mp2t. Never heard of that before. Tried downloading it but it wasn't a video file and it never loaded. Not sure if it was my computer having it's own networking issues or if it's NicoNico themselves.
Also I didn't know that BilliBilli actually had link download sites that worked