Humanity After the Fall

Post-Apocalyptic Man 「破滅後のニンゲン, Hametsu-go no Ningen」 is the second chapter of the Owari no Seraph manga.

Summary
Chapter 2 : Four more years had passed after that horrible night, and young Yu had become a foot soldier in the Japanese Imperial Demon Army. Every bit as brash and hot-headed as he was when he was 12, the young man is ambushed in the streets of Shibuya by a Horseman of John, a mysterious monstrosity that appeared after the world ended. There are countless numbers of these Horsemen roaming the night, but Yu simply brandishes his sword and cleaves the fiend in half.

The next day, he is put on suspension for disobeying orders in the middle of a fight. During class, he meets a strange and spritely girl named Shinoa Hiiragi, a surveillance officer sent by the Army to keep an eye on Yu and try to curb his delinquent tendencies. She informs him that unless he starts making friends and demonstrates he's capable of listening to others (using teamwork, not ignoring orders, etc), his suspension from the Army will be extended. Though Shinoa is Guren's proxy, it would appear that the impish girl derives most of her entertainment from making mischief, as Yu suddenly stumbles into one messy situation after another by that girl's design. Yu soon meets with a timid young boy named Yoichi, whom is targeted by bullies in his class. Yu decides to look after the boy, perhaps out of pity, and comes to find out that Yoichi is trying to befriend the bullies because he thought it might help him get into the army.

The next thing they know, the room their class was in explodes, and they learn that a vampire that had been kept in captivity had suddenly escaped. Yu of course makes a beeline for his classroom, and happens on the vampire as she had just begun feeding on a student. The vampire seemed to only be a child, but it made her no less dangerous. Yu draws his sword and dashes at the vampire, their fight raging all over the ruined classroom. Thanks to Yoichi restraining the vampire, Yu managed to cut her arm off, but wound up falling out the window with the vampire falling upon him. Right as the girl was about to finish him, Guren Ichinose cuts her down from behind in a single stroke. Yu awoke some time later in a hospital bed, with Yoichi and Shinoa sitting at his bedside, with the good news that he had officially been accepted as part of the taskforce responsible for hunting vampires: the Moon Demon Company.