Uh, I`m sorry if this is not where it`s supposed to be.
Two finds that I wanted to kind of share.
One is a 14 minute, 21 MIDI? ear-copied medley.
http://www.nicovideo.jp/watch/sm2515783
The other is a mini-project they have with various artists. I don`t know if they still are working on it, and/or if it`s just a compilation or a actual project.
(So it`s not a single circle.)
http://www.nicovideo.jp/watch/sm8341816
After reading descriptions and tag, the first video is under the
samidare tag.
Basically, (assuming my translation capacoty didn't fail me) a samidare are midis of touhou music done by hear, trying to get as closs as possible to the original.
Fist link is a video of such a samidare where the author made a medley of 21 touhou melody which also include at least 3 ending themes at the end.
The video was apparently popular enough to generate related videos and by extension a tag,
the Touhou 21 songs medley.
About the second link, basically, there was a project where people posted their own videos which must follow a specific theme :
starting and ending with a circle (Japanese version mention the term "Baton Pass)".
Afterward, they were made into a single video and music was added.
Interestingly, said video also have the samidare tag. ^^
Perhaps that for details it would be better to ask the person directly so here is its nico nico profile page :
http://www.nicovideo.jp/user/1680428Also, welcome here. ^^