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.
And so she causes problems.
Und so verursacht sie Probleme.
Y eso causa problemas.
Y eso causa problemas.
Et c’est ce qui engendre les problèmes.
E assim, ela causa problemas.