...Kind of an unrelated question, but what does @tos mean? I see it all the time.
@ing someone on Twitter means the tweet is directed at only one person; it's basically just a reply. If you're not that person, you have to go seek out the reply on OP's Twitter account to read it. It doesn't show up on their front page, only in the "Tweets and replies" or "Media" section if it includes a picture, so you might be scrolling a bit.
@tos automatically redirects to Twitter's terms of service. It's not a real account, but it still behaves the same way as a real account due to the nature of Twitter. That means if you @ it, it's hidden from your main timeline and only directed at @tos. If other people want to read it, they need to go seek it out directly.
People @tos for all kinds of reasons; maybe the picture is a spoiler, maybe they don't think it's their usual quality, maybe they think it's a fandom they're embarrassed to be drawing fanart for. Whatever the reason, it hides it from the public eye of their followers and makes it so you need to be very dedicated in combing a fanartist's account to see it.
tl;dr: It's just another way for artist's to hide spoilers or things they don't want to put on their main timeline on Twitter. Hope this explanation wasn't confusing.