The story of “Introductory Chapter” begins around the second half of October with Haruki Kitahara and Takeya Iizuka troubled by the fact that all the band members they gathered for the school festival have left.  The school idol, Setsuna Ogiso, invites Haruki to Karaoke. There, she sings to him the love song “Shin Ai,” and later her favorite song “White Album.” After the pianist Kazusa Touma and the singer Setsuna Ogiso are recruited into the light music club, the three of them play together at the school festival  and they perform Yuki Morikawa’s “White Album,” Rina Ogata’s “Sound of Destiny,” and an original song named “Todokanai Koi.”  When the day draws to an end, Setsuna finds Haruki and then confesses her feelings to him and the two of them start going out together. 
 Ah, what should we do, Haruki? It’s down to just you and me now…
 Ah, for the song we performed just now…let me introduce it to those that are not familiar with it just in case. / It’s called “White Album”, from about ten years ago or so I guess… it’s Yuki Morikawa’s debut song.
 It’s an original song we just completed yesterday.
 The title is… “Todokanai Koi”
 So I… well, um, I… I’m going out with Setsuna.
Because they hadn’t seen each other for a very long time, Kazusa’s mother, Yōko Kazusa, decided to attend her daughter’s performance at the school festival. While watching she notices Kazusa’s love for Haruki.  A while later, Yōko talks to a heartbroken Kazusa and tells her it was obvious the other girl would steal the boy.  The reason for this, Yōko said, is that the other girl is cute and had been very upfront about her feelings for him during the performance.  Yōko explains that she too has been thrown away by men, particularly by Kazusa’s father.  She asks Kazusa whether she wants a handkerchief and tries to calm her down.  Once she’s stopped crying, Yōko offers Kazusa the chance to go to Vienna with her to become a pro pianist even if it’s just because of her heartbreak. Yōko insists she doesn’t mind if she only does it to try to forget the man she loves  and gives her some time to decide.
 And you were flirty with that guitarist boy…
 So she stole him from you, huh?
 Well, it cannot be helped. She is pretty cute, after all. She was being open and direct about it, too.
 What are you saying? I’ve been thrown away too, you know? By your father, for example.
 Before I knew it, you became a girl who cries over love. My Kazusa, huh…
 I do not mind if it is to forget a man.
Some time after the concert, Kazusa drives Haruki and Setsuna to the hot springs. Upon their return, Haruki and Setsuna kiss each other before going home and there she confesses to him that ever since they started dating, when she declared her love to him, she has become a bad girl.  At the exact same time Kazusa is driving home, howling over her broken heart. 
 Hey, what should I do? Ever since I started dating you, Haruki-kun… I’ve been becoming more and more a bad girl…
 … If it’s for you, Haruki-kun, I can become even more of a bad girl… I’m starting to feel like that, you know?
 Aaaahh~! Aaaaaaah~ Waahaaaaaahaaaaah! Waahaaaaaahaaaaahaaaaah!!!
Later, Setsuna decides to host a birthday party at her place.  While en route to the party, Haruki remembers how much Setsuna wanted everyone to attend  and becomes concerned about whether Kazusa received the invitation, so he goes to her home to find out. Unfortunately, Haruki doesn’t know that Setsuna, despite being worried about what’s gonna happen to her relationship with Kazusa if she doesn’t happen to show up on her own,  hadn’t invited her or anyone else other than him and is happily planning the birthday party  while saying, ‘Just the two of us.’  Takahiro, however, does suspect she had invited just one person  but, considering the implications, he decides not to say anything to their parents. Setsuna was expecting to have sexual intercourse with Haruki.  This aspect of the story is not revealed to Haruki until the later installments of the series when Setsuna tells him she has been waiting ever since her 18th birthday to give her body to him and when she mournfully informs Haruki about wanting only him there for her birthday and his mind snaps back to her insisting on everyone being there that day.
 Let’s have a party with everyone, why don’t we?
 If at all possible, I’d like to celebrate with everyone.
 Hey, Kazusa… If you don’t come… I don’t know what will happen between us, okay? Because… I don’t think I’d be against it at all.
 Alright! … Okay. It’s done, it’s done♪
 Just the two of us.
 Are you really inviting all your classmates? Could it be [R Kitahara-san alone] that you actually only invited one person?
 For the bra… Would front hook or back hook be easier to undo?”
Later, Haruki finds Yōko Touma and explains to her that Kazusa is supposed to go to a birthday party. Yōko tells Haruki that Kazusa will be living with her next month and that she will not make the party because her plane arrives an hour after the party starts. But Haruki doesn’t give up and goes to pick up Touma at the airport and tries to convince her to go to the party.  The two get into an argument and Haruki asks why she hadn’t mentioned she was leaving.  Kazusa says it is him who disappeared from her sight by going somewhere that she couldn’t reach.  Kazusa runs from him, but not before the two confess their love for one another and she tells him that it had been a nightmare to have him so close but never being able to truly have him. While Haruki admits that he also loves Setsuna,  he says he had fallen in love with Kazusa first and was unaware that she had loved him all this time. Kazusa tells him that knowing he had accepted another girl had torn her heart to shreds every single day.  They kiss, but Kazusa gets mad at how good he is at it, having kissed Setsuna countless times, and in the end she runs away shouting how much more far behind Setsuna he wants her to be. 
 I’ve come to pick you up for… Setsuna’s birthday party.
 I’ve talked with her. Starting from the next month, you’ll be living with your mother… and that you’ll be going off to Europe.
 Why didn’t you come talk to me about this at all? Why, why… Touma!
 Aren’t you the one that disappeared in front of me!? Aren’t you the one that went to a place that I couldn’t reach!
 But if you ask me… whether I like or hate Setsuna, isn’t it a given? Of course I like her.
 Every day, every single day in front of you… having my heart shred to pieces…
 How many times have you kissed Setsuna already!? Just how far will you leave me behind until you’re satisfied!?
Meanwhile, Setsuna is left alone on her birthday because she hadn’t invited anyone, not even her family, other than Haruki. Then she receives a call from Haruki letting her know he will be very late because he is not feeling well.  Becoming worried,  she immediately offers him the alternative of celebrating on another day and with just the two of them.  But Haruki quickly rejects that idea and insists he will be there.  He also inquires if Setsuna knows what’s happening with Kazusa, and Setsuna answers she hasn’t contacted her.  Haruki, still believing her lie that she has invited a lot people, tells her to have fun with everyone else at the party  and Setsuna promises she’ll keep waiting for him.  However, he never shows up or calls her again that day, his excuse still being that he caught a cold.
 I’ll be late, but… I’ll definitely be there. Even if it’s after the party has ended, I’ll at least show up.
 A cold? The flu? You should be in bed, then!
 We can do it another day, okay…? Just with the two of us, like you wanted.
 It has to be today.
 No, she hasn’t even contacted me. She must be busy after all.
 I’ll definitely be there. Please start the party with everyone else and apologize for me.
 … I’ll wait for you.
Three days later, during the next meeting of the Light Music Club, Kazusa tells Haruki and Setsuna that she will be leaving for Vienna after graduation, which would take place next month.  Haruki pretends it’s the first time he’s heard the news.
 In any case, it’s been decided. After the graduation, I’m going to Vienna.
Despite the recent events Haruki does not break up with Setsuna during the weeks preceding Kazusa’s departure. The day before her plane takes off, Kazusa goes to school one last time, but she does not turn up for the graduation ceremony. Yet Setsuna finds a letter at the school from Kazusa so she knows she was there.  When Haruki is told about the letter he runs all over the city looking for her. In the end, his search is fruitless but, when he returns home, he gets a call from Kazusa and subsequently finds her standing near his house. Their meeting ends in sexual intercourse but also tears when Kazusa starts to cry. Yet she tells Haruki not to cry in front of her – the girl he threw away.  She goes on to tell Haruki that she bitterly regrets not having confessed her love to him before Setsuna did.  The next day, Setsuna convinces Haruki they should go together to see Kazusa off at the airport even though her departure would be sad for him.  At the airport, before she leaves Japan, Kazusa and Haruki kiss each other, which makes Setsuna cry.
 There was a letter inside my desk… it wasn’t there in the morning though.
 … Don’t cry. Not in front of the girl you threw away…
 … Regrets? I’ve had enough of them.
 Ah, haa, ahh… I, I should have said it. I shouldn’t have… tried to put up a strong front…
 Let’s go, Haruki. It’s not yet over for the three of us.
The chapter ends with Setsuna embracing and consoling Haruki after Kazusa has departed. Because Haruki does not ‘shake her off’ while she embraces him, Setsuna still has a twinge of hope that he will eventually accept her feelings for him. 
 Do you know that I’ll have to end up making the worst possible assumption, that you’ll accept me despite all your grief?