Ganpuru: Gunman's Proof

The year is 1880. Two meteors fell on Earth on a small island near North American Pacific Coast. In the middle of the island there is a small town governed by a sheriff. At first, the town's inhabitants didn't pay attention to the meteors. But then, strange things started happening. Monsters attacked people, and left on the victims' bodies a mysterious crest with one word: demiseed.