The relationship between Arima and Yukino had a rocky start, but they eventually come to an understanding with each other. Together, they learn to get rid of their masks and be happy with their true selves.
At first, Yukino hated Arima with all her guts, and understandably so, because he took her spot at the top, and it was a major blow to her pride. After 15 years at the top, she had never faced such a humiliating defeat, and was determined to take her rightful spot at the top by taking him down.
But Arima ends up getting a crush on her, and makes attempts to hang out with her. Of course, talking to Arima is the last thing she wants to do, but Yukino has an image to keep up, so she plays along and keeps on smiling even if it kills her.
She studies even more obsessively than usual, and to nobody's surprise, she gets the highest score on the midterms. In her mind, she gleefully imagines the look on Arima's face when he sees the results, and laughs evilly at having finally defeated him. But to her shock, he is happy for her, leaving Yukino confused. She comes to the realization that he was the real thing, while she was just a fake, and feels ashamed of herself for being such a brat.
When Arima later confesses his feelings for her, Yukino is quick to reject him. Finally satisfied, she brags to her sisters about her victory in her rivalry with Arima, because in the game of love, the adored one has all the power. But her sisters make her realize that while she was obsessively plotting his defeat, maybe she was actually in love with him. But oh well, it was too late for that.
But soon after, Arima catches Yukino in her true form, and blackmails her into becoming his lackey. Although Yukino is beyond humiliated, during the time that they spend together, they slowly get to know each other and discover they have many things in common. She was falling in love with him, but she didn't know how he felt about her, now that he knows how she really is like.
Yukino began thinking that Arima was just using her to do his work for him, and was upset. She angrily quits being his puppet, but Arima chases after her and they manage to work things out. Arima admits that he never meant to hurt her, and that all he wanted was an excuse to talk to her. After that, they became best friends.
With the blackmail days over, Yukino thought their relationship would finally start progressing, but lately, he was avoiding her. It all began when they both brought each other to meet the parents. Arima's parents were very kind and polite, and welcomed Yukino warmly. Then when Yukino brought Arima to her home, her family embarrassed her in front of Arima, and she blew up at them. Arima had been avoiding her ever since.
When Yukino goes to confront Arima about it, he pushes her away. She is hurt, and goes out of her way to give him the cold shoulder at school. He finally talks to her and explains everything. He reveals his painful past, and admits that he tried to run away from her because she makes him remember his past without even trying. He confesses that he might also be a fake, and how he feared he might be just like his real parents.
Yukino gives him a good punch in the face, and when Arima blows up at her, she tells him that she likes the real Arima better. Together, they promise to drop their perfect act and start acting how they really feel from now on.
BUT, they still weren't officially going out. Yukino wants their love to be mutual, but blew her chances both times Arima confessed his feelings for her. So she cooks up all these plans to catch him alone so she can confess her love and they can be the perfect couple. But her plans always fail, and she's about to give up.
The opportunity finally presents itself, and she's about to confess, but hesitates. She begins to doubt how he feels about her, and realizes that maybe it was too late for her to confess. She doesn't want to lose his friendship, and consoles herself by reasoning that being his friend is good enough.
While walking home, Arima tells Yukino that he still doesn't know how she feels about him, and that he was waiting for her answer. Yukino wants to confess so bad, but all her earlier doubts and insecurities were clouding her thoughts, and she runs away in tears.
At home, her sisters give her a pep talk and concluded that she was afraid of getting hurt. Yukino realizes that she has to be brave, and that if she was going to get hurt, then she wants Arima to be the one to do it.
The next day, she agonizes over how she was going to tell Arima, and figures if she can't tell him, she'll show him. Yukino reaches for his hand, and Arima is surprised at first, but he blushes and holds on... That day, they finally became boyfriend and girlfriend.