Kuroki chi no kyodai

Vampire Jirou and his brother Kotarou set sail to Yokohama. Kotarou being a restless kid starts wondering around the boat and stumbles upon a fight between the suppression team, and the vampires. Jirou comes to stop the racket, but a grenade knocked Kotarou off board. Jirou dives after him but due to his blood, water injures him.