Episode 20 of Re:Creators features something marvelous: real-world fanart of Altair from Pixiv appears in the show-world as fanart of Altair on "Piclive". For example, this screencap...
...depicts this piece of fanart uploaded to pixiv back in May by artist Mochizuki Kei (望月けい).
A few seconds prior, a number of other pieces of fanart are shown:
(Note that while all the linked images are SFW, Pixiv itself contains heaps of NSFW content.)
My question: how did these pieces of fanart come to be integrated into the anime? Were they "planted" ahead of time (i.e. did the artists have a prior arrangement with the producers to draw and release this art earlier in anticipation of episode 20)? Or was this art drawn "organically", with the artists only later being contacted about using it in the anime?