"Black Blood Brothers" is a 12-episode anime series set in a world where vampires, known as Kowloon Children, coexist with humans after a devastating war between the two species. The story centers on Jiro Mochizuki, a powerful vampire from the Kowloon Bloodline, and his younger brother Kotaro. Jiro is a former hero of the Kowloon Conflict, a war that nearly eradicated the vampire race, and now seeks a peaceful life while protecting his brother. The siblings travel to the Special Zone, a sanctuary where humans and vampires live together under strict regulations, to escape the dangers of the outside world.

The Special Zone is governed by the Compromisers, a group tasked with maintaining order between humans and vampires. However, the sanctuary is under threat from the Kowloon Children, a faction of vampires who seek to dominate both species. Jiro and Kotaro become entangled in the conflict when they encounter Mimiko Katsuragi, a human Compromiser, and Cassandra Jill Warlock, a vampire noblewoman. Together, they must navigate the political tensions and supernatural threats within the Special Zone.

Jiro’s past as a warrior and his unique abilities, including his mastery of the "Silver Blade" technique, make him a key figure in the struggle against the Kowloon Children. His relationship with Kotaro, who is unaware of his own latent vampire powers, adds emotional depth to the narrative. The series explores themes of brotherhood, loyalty, and the consequences of war, while maintaining a focus on action and supernatural intrigue. The plot unfolds through a mix of episodic encounters and overarching conflicts, culminating in a confrontation that tests the bonds between the characters and their resolve to protect the fragile peace of the Special Zone.