"Hey, let's fight!"
Ka-Ge-Ki is a game, where you play a fighter out to get revenge on the Kageki gang for murdering his brother.
"Is that all?"
Well, you have the ability to throw two different types of punch and to jump. Only the big punch is used. The gang is very polite and allows you to beat them up one at a time.
"Oooh, he not bad."
What's a referee doing in a gang anyway?