トワイライトハンターズ

One day you picked up a ring that was your grandmother’s…that was the start of the frightening days to come. Someone suddenly attacks you and all you can see amid the darkness is a pair of glowing fiery eyes. Four vampire hunters come to your rescue just as you are on the verge of death. However, you get bit by a vampire when you lower your guard, causing you to begin transforming into a vampire yourself… [From iTunes page] The game is free, but requires "story tickets" in order to proceed throughout the story. "Story tickets" are given every day, or by completing the task from its sponsors. You can also play the game without "story tickets" by simply purchasing the scenarios.