Owari no Serafu

Owari no Serafu or Seraph of the End is the second vampire manga I've read, and this is a lot different to Vampire Knight, which is also good. The setting for this one is different, as part of Japan has been infected by a virus which only affects those over the age of 13, and vampires have taken over as a result. Because of their immunity, children under the age of 13 have been taken by the vampires as livestock to help quench their thirst for blood.

Owari no Serafu follows Yuuichirou, a child who was put into the Hyakuya orphanage at the age of 8 and has a strong hatred towards vampires, which is what we see when the story begins. There he became part of the family of children there after wondering why the eldest child known as Mikaela (or Miki) wanted to be his friend whilst he was being mean to him. He, along with the rest of the Hyakuya family, are taken by the vampires after their director becomes a victim to the virus. Later on there's a plan to escape the orphanage which, though successful for Yuuichirou, turned out to be a massacre for the rest. But Yuuichirou discovers that the vampires lied about mankind being wiped out by the virus when he escapes the vampire hideout and is taken in by the leader of the Moon Demon Squad - the vampire annihilation force.

We see Yuuichirou's journey begin four years later, when it looks like he's become an experienced vampire hunter until the truth unfolds after he successfully kills one of the Horsemen. But then it turns out he's not actually part of the squad yet and must make friends at the school he is attending in Shibuya before he has a chance to join. He is successful when he kills a vampire let loose in the school to prove that he is worthy of being in the squad, and makes a friend in the process! And from there his journey begins.

Owari no Serafu does use a generic formula though, where the main character has a strong dislike towards the new changes in his/her life and vows to vanquish the evil which has affected his loved ones in their attempt to make the world a better place. It does mean that some things do become predictable which can make or break it. Having seen comments on a few sites, people aren't exactly enjoying this one. Not that you shouldn't give it a miss - try it out and see for yourself. Boku no Hero Academia is another manga which uses a generic formula but is much more successful with it by setting the story in a world full of heroes and villains. I recommend checking that out because it did make for an interesting read.
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Summary

After losing his loved ones in a horrific attempt to escape from vampires, a young boy uses his hatred towards them to fuel his drive to wipe them out and find a cure for a virus that only affects those over the age of 13
Anything else: Because of the generic formula, things are quite predictable from the beginning