Black Blood Brothers

Black Blood Brothers summary:

During a War called the Hong Kong Crusade, an Old Blood vampire, Jirou Mochizuki, aka the Silver Blade (Gintou), fought and defeated most of the Kowloon Children.
Ten years later, Jirou heads to j.a.pan with his little brother, Kotarou, in hopes of reaching The Special Zone, a thriving secret city where vampires live. They soon realize that a plan to infiltrate The Special Zone is being hatched by the Kowloon Children survivors.
As they travel to The Special Zone, Jirou encounters enemies from the past and new threats that may endanger the safety of the Special Zone. The abduction of Kotarou, by one of the Kowloon Children, thrusts him even further into the battle.