Zoku Gosenzo San`e 4

So Gen is back from America and everyone is happy to see him. All of the girls missed him a lot. But it's too bad that his condition has not improved even with all the treatment he obtained. He wasn't able to cure his illness and to make it worse, a lot of very strange occurences have begun to occur in the school. People are fainting from loss of blood and vampires have appeared. Now it's up to Gen and his friend to solve this mystery.