I have had this theory that ooki-san is a 4th wall breaker. I mean, it does make sense. In the very first chapter, chapter 0, she was talking to the reader. On top of that, she told the delinquent character that there cant be 2 ‘characters’ of the same type. So, i dont think ooki was just stalking katigiri and okada.
Also, the first year girl looks like ooki, righttt?? Are they sisters or something?