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 here because I'm genuinely worried 
about Fuyuki and Mamiya-san.
Estoy aquí porque me preocupan Fuyuki y Mamiya-san.
Estoy aquí porque me preocupan Fuyuki y Mamiya-san.
Estou aqui por estar realmente preocupado 
com o Fuyuki e com a Mamiya.