I started reading 'Red Demon Eclipse' because the art looked cool, and honestly the characters grew on me slowly. The protagonist is a guy named Ryo, who's this alchemist's apprentice with a tragic past—his village got destroyed by demons. His role is basically our window into this brutal world, and he's trying to find a way to use alchemy to fight back, which sets up the main conflict.
Then there's Silvia, a knight from the Church who hunts demons. She's the straight-laced, duty-bound type who clashes with Ryo's more emotional, desperate methods. She brings in the whole institutional power and dogma angle. A third key player is 'The Red Demon' itself, which isn't just a monster but almost a force of nature that both Ryo and Silvia are trying to understand or defeat. Their dynamic drives most of the story.