CLAMP is a very famous manga artist group who created X, Code Geass, RigVeda, Magic Knight Rayearth, XXX Holic, etc.
NicoNicoDouga lovers were AMAZED by a Miku music video with illustrations by CLAMP.
This is CLAMP's website
explaining [ja] why this collaboration was realized.
According to the article, CLAMP members were visiting recipe sites to cook, and found cooking videos uploaded on NicoNicoDouga. Watching the videos of people actually cooking (rather than just recipes) helped them a lot. They started visiting NicoNicoDouga site and found VOCALOID series including Hatsune Miku very interesting.
They wanted to create videos themselves too and found this music video of Hatsune Miku, which had a wonderful music but with no visual- the screen was just black for the entire video. It was created by MegaP, which was actually a very famous game music creator
Shinji Hosoe [ja] (created Ridge Racer Rotterdam Nation, Roteen da Moon, etc.)
CLAMP contacted him and got the permission to make illustrations for the music and posted on NicoNicoDouga.
There are LOTS of professionals playing with NicoNicoDouga- illustrators, manga artists, SF author, etc
and when the viewers recognize the fact that they are the professionals, they often get comments saying "Please get back to WORK!!"
CLAMP preempts by writing on their site:
"Work diligently. Play seriously 「仕事は真摯に。遊びは真剣に」 " :)