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.
in the grips of puberty, 
doesn't cross the line.
en medio de la pubertad, no cruce la línea.
en plena pubertad, no cruce la línea.
nas garras da puberdade,
 não ultrapasse os limites.