"Tokyo Ghoul: Jack" is a prequel OVA to the main "Tokyo Ghoul" series, set several years before the events of the original story. The narrative centers on Taishi Fura, a high school student who becomes entangled in the dark world of ghouls after a series of mysterious murders occur in his district. Taishi, initially a delinquent with a strong sense of justice, investigates the killings alongside his friend Ryoko Fueguchi, who later becomes a significant figure in the main series.

The story introduces Kishou Arima, a young and highly skilled CCG investigator, who is assigned to the case. Arima’s calm and methodical approach contrasts with Taishi’s impulsive nature, creating a dynamic partnership as they uncover the truth behind the murders. The antagonist, Lantern, is a ghoul who preys on humans and uses his cunning to evade capture. Lantern’s actions force Taishi to confront the harsh realities of the ghoul-human conflict, challenging his preconceived notions of justice and morality.

As the investigation progresses, Taishi’s resolve is tested, and his interactions with Arima reveal the complexities of the CCG’s role in maintaining order. The OVA explores themes of coexistence, prejudice, and the blurred lines between good and evil, setting the stage for the broader conflicts in the "Tokyo Ghoul" universe. The narrative concludes with a decisive confrontation, leaving lasting implications for the characters and the world they inhabit. The OVA serves as a concise yet impactful exploration of the series’ core themes, providing context for the events and relationships in the main storyline.