I can never understand the reason people say the line 'they're coming'. It's like, 'I can see they're coming, mate, they're right in front of us. I'm not blind.' Do they say it just for the sake of it or something?
It's just a thing they do in story art (books, movies, tv shows, comics, manga, you name it). It's become kind of a trope, I guess. Helps fill out pages for mangaka, anyhow,