Minako, who was regularly bullied by her mother-in-law, ended up injuring her in an accident. Panicked, she ran away from home, changed her name to Marina Matsumoto, and started living and working at a factory. Despite being a woman, she managed to lead a peaceful life by doing heavy labor alongside the men. However, when a detective showed up at the factory looking for Marina, a worker named Fuchigami discovered her weakness. If she wanted to stay at the factory, she was forced to undergo obscene anal training, and eventually became a slave to the workers' sexual needs...