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.
Anyway, karaoke's all we've 
been doing for a while now.
Como sea, hemos estado cantando karaoke por algún tiempo.
Da igual, hemos estado cantando karaoke por algún tiempo.
Enfim, a gente não fez nada além 
de cantar há um bom tempo.