Alas, dunno why people tend to downplay Ruka's behavior. I know spoilers overblown her attitude, but still was a toxic move from her part to pull a Nino Nakano and go "Trial means jackshit for me, i love you bc it's FAAAAAAAAAATE!!" and then gaslighting his thoughts with the already obsolete "you a customer, she a rental" pretense. Like, seriously?? If you lose, you lose (or as Ivan Drago says: "if he dies, he dies"). Accept defeat with dignity and move on. She's only inches away from turnin into another salty psycho bitch straight up taken from a seinen drama romance manga.
Moving to Chizuru, i know she said she should do something, but what was shown here just tells me her insecurities regarding her feelings are just going up to her head and will make more drama. She doesn't know how to deal with her newlyfound feelings and said inexperience might bite, not only her, but also Kazuya in their asses if a mischoice of words derivate in another bigass misunderstanding that either Mami or an unhinged Ruka would take advantage of. She seriously needs to find the courage to sort out her own feelings because, even though it's a novel thing for her, because working as a rental girlfriend isn't the same as legit dating with feelings being involved, dragging out things will only harm both her and Kazuya.
This time, Kazuya takes the cake, despite of dogeza'ing his way in the beginning (understandable, he knows how dangerous an unhinged Ruka could be if he aggressive and bluntly tells her off
See chapters 26-27 to understand what am i talking about), he manages to handle her bullshit like a true chad and found his resolve to confess or die fighting. He's also ready to atone himself for the lies just in case he gets rejected by Chizuru, so in a sense, he's also ready to move on if things go south. That's quite remarkable. His 16,6 cms monster is also a remarkable thing. The girl he ends up legit dating in the end, be it Chizuru or not (but not Ruka or Mami) will be lucky to have such a stud.