We’ve seen most of the episodes several times by now, but I still didn’t notice this girl until she was pointed out to me. She’s been dubbed Scarf-tan, Scarf Girl and Miss Waldo and she’s always where things happen, but is she just a terribly unlucky girl or maybe a Hero TV employee? She’s not the only background character that’s appeared more than once, for example the drunken man at the bar in episode 4 appears again in another episode among the crowd of spectators.
As far as photobombing goes, she’s a lot more inconspicuous than Origami Cyclone
in the background. I wasn’t able to spot her in episodes 2, 3, 4, 6 (added in BD) and 23, but she’s been in all the others.
Personally, I think she’s a running gag and a jab at some TV series always using the same extras. Although her design is pretty plain it’s more detailed than most of the background characters we see at the crowd scenes so reusing her is definitely intentional. I will laugh if it turns out that she has an own character page in the upcoming official books. (In fact, I’m secretly hoping for that to happen!) Update: She did get a page in Official Hero Book!
Oh and if you’ve spotted her in the episodes I couldn’t find her in, do drop a comment!