Inner Demon

In the daytime, Hollowfort seems like a normal steampunk town. But at night, monsters roam the land with evil intent. Hollowfort is guarded by a demon who fights any creature who dares to set foot in it. But no matter how many monsters he fights, no matter how many lives he's saved, the people of Hollowfort reject their dark vigilante for his species. Little did they know that there's more to him than they'd realized. Who is this noble entity and what's his story?