From MangaHelpers:
This is a continuation of the story of Higanjima, featuring an isolated island surrounded by fish demons and a population of warring vampires and humans. Ryousuke, his girlfriend Kazumi, and his friend Yamaoka are shipwrecked by the fish demons and wash up on the shore of this cursed island. They soon encounter the inhuman cruelty of the vampires first hand, before Ryousuke is able to meet up with the human resistance. Ryousuke wants nothing more than to escape the island, but mainland Japan may not be safe for long. If the humans don't defeat the vampires soon, then the vampires will succeed in their plans to spread the virus to the mainland.