Koko Ninna-Nanna is a young and energetic Melos Warrior who serves as the leader of a resistance group she describes as an armed theatrical company, dedicated to opposing the monsters that dominate human society. Despite her youthful appearance, Koko demonstrates greater tactical intelligence and combat maturity than the series protagonist Bocca Serenade, and she balances her warrior discipline with an adult sense of humor that serves as a coping mechanism for a tragic past she carries with her. Her motivations are rooted in the fight against the monster-run world, and she actively directs her insurgent cell in skirmishes and sabotage operations. In the story, Koko acts as both a seasoned ally and a foil to Bocca, often outthinking him and guiding him through the dangers of their conflict. Her key relationships include her fellow Melos Warriors, particularly Bocca, with whom she shares a bond forged in battle, though she remains somewhat enigmatic about her own history. Throughout the series, Koko’s development unfolds as she continues to lead her group while confronting the lingering effects of her past, using her wit and combat prowess to protect those around her. Her most distinctive ability is her Four Card attack, named after a strong poker hand, and like other Melos Warriors she wields an Aibar machine. Her last name, Ninna-Nanna, is the Italian word for lullaby, reflecting a softer undercurrent beneath her playful and sometimes intense demeanor.