They hang out as friends often in the show and manga. Combine that with yuri goggles, and there's your answer. Well, not only yuri goggles; there is some fanservice too, like Chiri taking various fetish pictures of Harumi in a school swimsuit and such.
No, it happens that Chiri knows Harumi's brothers goes to animation studios and she is following the same path making fun of her and at the same time making her look pityful, when that was supposed to be a secret.
BakaHoushi said: I'm not quite sure where the rivalry between these two comes from. They're popular together in fandom as both a couple and as rivals, but why?
They're childhood friends. Chiri saved Harumi from a paedo in chapter 182 when everyone else were too apathetic to help or call for help. A start of a beautiful friendship in a way, I guess.
