Cicada is Lucciola's older brother and Maestro Delphine's most skilled Guild Agent. He puts his formidable martial arts talents to use as her personal bodyguard and assassin.
He and Lucciola were born into a lower caste family and appeared to be owned by the Maestro. Due to his age (33), Cicada was likely forced to participate in the Rite of the Covenant when he turned 17, and probably brainwashed into subservience to the Maestro (like Dio was during the rite), which would explain his total lack of empathy or qualms when confronted with the prospect of killing his own brother.
He prevents Alex Row from killing Delphine when the Guild boards the Silvana. However, Lucciola kills him in combat in front of Delphine after Claus, Alvis, and Dio escape from the Guild stronghold.