Serge is the leading protagonist and narrator of Radical Dreamers: Nusumenai Hōseki. Like adolescent protagonists from other stories, Serge tends to be clumsy and outspoken. He has a sincere yet playful crush on Kid, who, as a way of flirting, constantly belittles him about his lack of fighting ability and his proneness to make bad jokes. Serge began his free life as a traveling musician, wandering city to city in a nomadic lifestyle. He wrote many songs, including the one in Riddel's music box, "Distant Promise." Kid implies that it was one of Lucca's favorite lullabies.