Haruki hears about Kazusa's moving from her mother, who she hadn't been on good terms with.  He feels betrayed and angrily confronts her.  But his words force open the door to Kazusa's heart, which she had desperately tried to keep closed so that the three of them could stay together.
You're just playing chords, right?
Du spielst nur Akkorde, richtig?
Solo presionas las cuerdas, ¿no?
Si solo estás con acordes, ¿no?
Il suffit d’appuyer sur les cordes.
Você só está segurando os acordes, não?