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.
If adults like us don't do it, who will?
Si nosotros como adultos no lo hacemos, ¿quién lo hará?
Si nosotros como adultos no lo hacemos, ¿quién lo hará?
Se nós, adultos, não fizermos
 isso, quem o fará?