The World of Blood Legacy

Blood Vessel World 「血脈のセカイ, Kechimyaku no Sekai」 is the first chapter of the Owari no Seraph manga.

Summary
In 2012, the world allegedly comes to an end at the hands of a human-made virus, ravaging the global populace and leaving only children untouched. It is at this time that vampires emerge from the recesses of the earth, likely followed by age-old horrors of the dark thought only to be myth. The vampires sweep the earth and claim it in a single violent stroke, subjugating the remnants of humanity and leading them beneath the surface to safety. This "protection" comes at the price of donating blood to their captors, which leads us to the beginning of this story.

Yuichiro Hyakuya  is a member of the vampires' "livestock" in the underground city of Sanguinem, just beneath Kyoto. He lives there with the orphanage he was inducted into, just before the viral outbreak 4 years earlier. Among the children is another boy the same age as Yu, named Mikaela Hyakuya (nicknamed Mika) and a girl named Akane. These three watch after the rest of the children, whom are too young to fend for themselves. The boys are polar opposites in personality, with Yu being brash, impatient and preferring to be alone, while Mika is bright, intelligent, smiling brightly and making all the children feel safe and protected around him. One day, as Yu muses about having to give blood to his captors and brags about how he plans to slay them all someday, he and Mika run into an unhooded vampire: a Noble by the name of Felid Bathory. Mika gleefully calls after Felid and runs to him without a hint of distrust, with Yu watching as the vampire caressed his cheek. Mika agreed to meet Felid at his mansion later on, with Yu having to find out firsthand that his best friend had been meeting illicitly with the vampires he so loathed. Mika tried to explain that doing this entitled him to certain advantages, but Yu refused to listen and stormed off.

Later that evening, after the orphanage enjoyed a much tastier and more substantial meal than usual, Yu awoke to Mika creeping into their sleeping quarters. Though Yu was still mad at Mika, he became immediately concerned when he sensed just how much his visits at the mansion were scarring him inside. However, rather than letting Yu press the issue, Mika sidestepped the matter and showed his friend some things he had purloined from his visit - a handgun, and a map. The two woke up the other children, setting off to escape Sanguinem that very night.

At the gates of the city, just at the threshold of their freedom, the children are cut off by a single interloper - Felid Bathory, who was waiting for them. With the carnal ferocity of a total psychopath, the Noble leaped down at the children and set to work slaughtering them barehanded in front of Mika and Yu's eyes, just for the sadistic pleasure of breaking his young thrall Mika's spirit and stomp out his hopes of escape. The two fight back, but Mika is mortally wounded as Yu just barely manages to sneak a shot in Felid's head with the gun he stole. They had won the fight, but at too great a price. Yu was now surrounded by the lifeless stares of dead children, and his best friend Mika lay bleeding out, knowing in his heart that the cruel mass-murder of his family was all his fault. At Mika's urging, Yu runs out through the gates as the only survivor of the Hyakuya Orphanage. He meets up with a platoon of human soldiers led by a man named Glen Ichinose, whom had formed a core of resistance against the vampire menace, and thus Yu's quest for revenge against a race of nightwalkers begins in earnest.

Chapter Notes

 * Yūichirō Hyakuya and Mikaela Hyakuya are introduced.
 * According to a book:
 * Vampires can be killed if you shoot them on the head or if you remove their armband device as they can be killed by ultrasonic waves.
 * The physical strength of a Vampire is 7 times that of a human.
 * Vampires allow the kids to live in exchange of their blood.
 * Mikaela lets Felid Bathory drink his blood and in exchange he buys him anything he wants.
 * The kids met each other four years ago in the Hyakuya Orphanage.
 * Yūichirō ended up in the orphanage because his father tried to kill him and his mother spread a rumor that he is the son of a demon, then she lost her mind and she killed herself. Mikaela ended up there because he was kicked out of a moving car by his abusive parents and was taken in by the orphanage.
 * The virus hit the Hyakuya Orphanage, which the Director contracted. Blood suddenly began to pour from the directors mouth and nose leading to her death.
 * Vampires attacked the city and a lethal virus spread among humans who were older than 13.
 * The vampire troops were under the direct command of the third founder Kururu Tepes.
 * It was announced by the vampires that from that day on the children would be in their charge.
 * Mikaela steals a gun and a map showing the way outside of the underground world from Felid.
 * The kids attempt to escape but Felid was waiting for them.
 * Felid murders all the children except Yūichirō who shot him in the head with a gun.
 * Yūichirō escapes from the underground world and reaches the outside world alone. There he finds a man with two women who asks him if he will help them exterminate the vampire race, Yūichirō accepts.