Shock... Anger... Sadness and then loss...
Robin experienced all kinds of emotions during Billy's short speech.. The short speech that he felt was never going to end.
He tried to clench his fists a few times and open his mouth to yell at Billy, telling him that he didn't care about his words and that he would finish what he started!!
But no sound came out of his mouth.
How does he not care!? Every word that came out of Billy's mouth hit his heart like a war hammer... The anger, the killing intent, and the indifference towards life disappeared as if it had never existed.
Robin looked behind him at his massive army of Demons, perhaps in their cruel faces and the bloody aura he again would find the determination that he feels as it comes out of his body like sweat...