If you're looking for manga similar to Seraph of the End: Guren Ichinose - Catastrophe at Sixteen (Light Novel), you might like these titles.
Karin Maaka can bite a throat like a proper vampire, but where others of her kind need hot red blood, she has too much of it! Every month, she's compelled to inject blood into her victims the way a snake injects venom. And her handsome classmate Kenta Usui makes her feel like she's is going to spurt blood like a geyser. Talk about embarrassing! When Karin's latest victim turns out to be as rich as he is good looking, it causes hilarious chaos at her school. Will she ever live in peace?
Doppo Kunikida is an idealist and a strait-laced detective at the Armed Detective Agency, an organization that takes on dangerous jobs that even the police won't handle. Everything in his life is progressing as planned until one day he's ordered to watch over the new guy, Osamu Dazai, a suspicious fellow of unknown origin who is obsessed with the thought of suicide. While investigating an unusual case involving a so-called haunted building, they find several of the missing people from another investigation. However, before they can find out how these cases connect, they are attacked by the mafia's Ryunosuke Akutagawa, sworn enemy of the agency! This is the beginning of a hopelessly inseparable relationship between two detectives. A battle of Abilities erupts in the shadows of Yokohama!