She doesn't use any form of rationalization to convince herself that she is justified in harming others; the pure enjoyment she gets from doing so is reason enough.  The other bullies are the only people that she feels comfortable being "her true self" around.When Hoshiko and the rest of the bullies are ganging up on a victim, Hoshiko often tries to convince the other bullies to do things like burn their victim with lit cigarettes. The other bullies always have to talk her out of it. 