Shun's younger brother Fuyuki and his girlfriend Mamiya-san kissed.  When Shun finds out, he asks his friends what he should do as Fuyuki's older brother.
Fuyuki ignores his brother and goes on a date with Mamiya.  The gang decides to follow the couple on their date and end up at a karaoke box.
That's not why I gave you one.
No es por eso que te di uno.
No es por eso por lo que te he dado uno.
Eu não te dei presente por isso.