Ruka is a girl that from the beginning comes off as incredibly overbearing, incredibly clingy, and very possessive.
Time rolls around to Kazuya's birthday and after finding out when Chizuru's birthday was his grandmother insisted that it was going to be a double birthday party for them now. Chizuru reluctantly agreed but said her grandma was in the hospital so she would need to go there first. Trying to keep it on the downlow Kazuya says that he'd celebrate with Ruka on the Sunday after his party, but he accidentally says that Chizuru would be coming to his place with the family. Ruka shows up to his house uninvited and inserts herself in trying to "be the girl that Kazuya's family wants; to be Chizuru". She's doing a fairly good job too buttering up the family; and upon learning that Mizuhara is going to be late/not be able to come she almost says that "she loves Kazuya more than anyone".......but right as she does, in to save the day, is Mizuhara Chizuru. She immediately radiates the energy that Kazuya's family loves from her. The biggest problem is what comes next and that is Kazuya's grandmother offers the engagement ring that was hers and then Kazuya's moms to her. Stunned, she doesn't know what to do, she's just pretending and can't accept it and Kazuya knows that she's in such a weird spot. He looks at Ruka and realizes that she's in a worse spot, because being his "technical girlfriend", she's seeing his family all over Chizuru and on top of that giving her a treasured family heirloom that people usually only give women they figure will end up being family down the road anyways. It's at this point Kazuya realizes that he has to come clean with his family, he can't put both these girls, particularly Chizuru in this spot anymore. He goes to the toilet before revealing all.
On his way to the bathroom and her way out, THIS HAPPENS..........
So I've seen a lot of people defend this move on Ruka's part saying that "she's just being assertive because that's her man", "Kazuya was sending mixed signals to her", "she's just trying to beat Chizuru", and more. Let me explain what this actually is and why there is no way you can possibly defend it no matter what you think it is or how it is.
It is SEXUAL ASSAULT, plain and simple. There's no way around it. The definition in the dictionary of sexual assault is "non-consensual touching of one person for the sexual gratification of another, including rape, fondling, molestation, or other unwanted contact." For anyone that is like "whoa, whoa isn't that a bit excessive like it's not sexual assault it's relatively harmless." Let me ask you this, IF that was Kazuya who pulled Ruka in or pinned Ruka to a wall and forced a kiss on her and then when she pushes away saying "no we shouldn't" and he did it again............what would you call it ?? You would call it sexual assault. So just because Ruka does it, doesn't make it okay, it doesn't make it playful, there's no justification to it. It's wrong. And even she says, "Sorry, I crossed a line there, but I don't want to lose. I have no regrets." THAT is not something you can just say after doing that and not get away with doing what you did. Yes, you don't want to feel inferior or whatever but still god damn you can't do that. When I saw on Twitter that someone said it was sweet that Ruka was making the first move on Kazuya because they are dating and he hasn't made any moves. Listen, even if they are technically dating, you can't put moves on your partner if they say they don't want to. I just don't get how people are willing to defend Ruka, even she said she crossed a line, like she admitted what she did was wrong. I understand that in a show like this everyone is searching for a "best girl" and it's between Chizuru, Ruka, Sumi, and Mami & people are willing to defend their "best girl" to the death. That's just the twisted way the anime/manga world works sometimes.
We're going to top all of this off with something simple, after all of this stuff happens, after all of the problems she causes and the sexual assault. HE FEELS BAD ABOUT TAKING HER FIRST KISS.........HE FEELS BAD...............BRO WHY SHOULD HE FEEL BAD AT ALL ????? I don't understand it and worst part is that..............Ruka actually gets WORSE.............