The "elite student in music room 2" turns out to be Haruki's delinquent classmate, Kazusa Touma.  With his characteristic pushiness, he tries to get her to join the light music club.  But his pushiness backfires, and only makes her more annoyed.  Setsuna gets irritated... no, involved, and approaches Kazusa secretly.
You could say she's 
the one who taught me.
Man könnte sagen, 
dass sie mir das Gitarrenspiel beigebracht hat.
Podrías decir que ella me enseñó.
Se podría decir que fue 
ella quien me enseñó.
Elle pourrait être 
mon professeur.
Pode-se dizer que foi ela quem me ensinou.