Secretly Greatly -

: A young agent who infiltrates a local high school . He looks up to Ryu-hwan as his hero and mentor.

: An agent posing as a rock star trainee, despite having no actual musical talent. Secretly Greatly

: The unit's top lieutenant who disguises himself as Bang Dong-gu , the village idiot. He perfectly executes his "fool" persona by falling down stairs daily and acting mentally challenged, all while secretly being a lethal combatant. : A young agent who infiltrates a local high school