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.
Even if her mom donated that piano,
Auch wenn ihre Mutter das 
Klavier gesponsort hat,
Aunque su madre haya donado ese piano,
Aunque lo haya donado su madre,
Mesmo que a mãe dela 
tenha doado o piano,