In his quest to find the elusive 'Karoku,' naive Nai clings to his only leads—a worn bracelet and a name. However, his journey takes a perilous turn when he catches the eye of a monstrous woman intent on making him her pet. Luckily, a resourceful thief named Gareki swoops in to rescue Nai from captivity. Together, they unwittingly become fugitives after a heist gone wrong, thrusting them into the shadowy world of 'Circus,' a powerful defense organization safeguarding the nation against flesh-eating monsters known as 'varuga.' As they delve deeper into Circus' mysteries and the enigmatic group Kafka, Nai's connection to Circus through the bracelet sparks intrigue. While Nai finds refuge within Circus, Gareki struggles to find his place among its ranks. Their pursuit of Karoku unveils a sinister pattern as malevolent varuga creatures swarm around Nai, intensifying their dangerous journey.