So...I had stopped browsing Pixiv in February and I went to it again a few days ago.
I decided to look all the Pokemon-related stuff I had missed during these 5 months (about 500 pages) and I noticed that around April/May, Pixiv users have been drawing shitons of Milotic/Wishiwashi/Charizard/Tyranitar.
Anyone knows what was going on with these particular Pokemon in that time?