Lol those two girls that we’re seriously about to bully the MC has the Gall to say that bullying the weak is a horrible thing to see when she was about to do so.
It's written Kokoro no Kintama
Literal translation: "the balls inside your heart"
Figurative translation: "The balls inside you", "The spirit of the balls"
I guess the closest translation would just be the slang term "He's got balls." but then you would have to shift the dialogue around to get the joke to land.