I am honestly a bit confused here... How and where do you see this story containing anything akin to rape? The guy was pushy and harassing, yes, but no more than that. The two main characters always respected each others wishes, never going farther than what was comfortable for both of them.
It seems a bit odd to call a guy who dragged a girl into a secluded area with her shouting "No" and "Let go of me" the entire way, threw her against a tree, and then tried to force himself on her as just "pushy and harassing" and no more than that. I mean, I guess we could be incredibly generous and assume that he wasn't going to actually do something, but generosity is typically something you don't want to give to someone who was clearly about to sexually assault someone.
Also, are we meant to believe that whoever took the photos just came straight to the company to hand them over? Because my first thought is that their boss has people following them around waiting to catch them if they dare slip up and engage in any activity that implies that they're not the property of their fans, who will also refuse to help someone who is clearly being forcefully dragged into a secluded area to be assaulted.
He is being pushy and harassing her. He fully deserves the slap and more, being a complete and utter douchebag. He fails to respect her "cut that out" and "stop - let go of me", which is deplorable and a real world issue that we see all too often. Still, those actions do not constitute rape. The distinction is important.
After the slap, lets go and does not follow her. It is a sad state of affairs that it takes that much to make him realise he stepped over the line, but even in western culture it is not uncommon for it to go that far. This is problem with the way all too many societies see us women as something to be conquered, and is even more pronounced in many Asian cultures.
As for the "idols being photographed" piece... That's an entirely different can of worms, one that is similarly infuriating. The whole "property of their fans" thing is pretty nasty, as the case of Minami Minegishi demonstrated. But that's a story for another day.