The underaged cosplayer community is kinda fucked when you think about it. That little middle schooler girl probably has hundreds of pedophiles jacking off to her pictures... Kinda bad parenting not gonna lie...
Now that I think about it.. yes.. it is indeed creepy. It may be hard to think about people that would get off to real children cosplaying but then you realize that they do exist, and some even going further than just that.
For anyone who is confused with the "ejaculating" bit I think he is saying" 写生 - shasei" which means sketching (as in the costume outline for the cosplay) which also have the same pronunciation as "射精 - shasei" which means ejaculation. I haven't read the scans but it is a possibility.