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.
I'm sure you don't need telling, 
but don't try anything, okay?
Estoy seguro que lo sabes, pero no intentes nada.
Estoy seguro que lo sabes, pero no intentes nada.
Eu sei que nem precisa dizer, mas não 
tente nada de estranho, tudo bem?