Tsukune Aono

For Tsukune, it's after he realizes that he is in a school full of monsters. When it has become clear that Outer Moka (whom every guy is instantly smitten with) has affections for Tsukune, every guy in the student body gives Tsukune the stink-eye and Saizo to antagonize him instantly, only for Moka to defend him. This establishes him as a Clueless Chick Magnet and an Unlucky Everydude who is completely outmatched by his monster classmates, but he is such a Nice Guy that the girls that flock to him are ready to fight on his defense.

Example of:
Establishing Character Moment