This obscure NES JRPG, Dark Half, You play as two characters whose stories are interconnected and switch whenever you finish the other's chapter.
The first protagonist is a silent, heroic warrior named Falco who aims to stop the demon lord. The second protagonist is the demon lord Rukyu, The Fallen One, and is the more interesting character. While Falco's story plays like a typical heroic fantasy, Rukyu aims to destroy all of humanity. It sounds simple, but there are interesting twists as the game goes on.
Anyway, Falco's side plays like a typical fantasy rpg where you have party members who can equip and forge items and cast spells. Rukyu is obviously different. He's a demon lord with high stats but is limited to casting powerful spells and has a party of AI-controlled monsters, whom you can recruit by capturing monsters in battle.
The game has a unique mechanic where you have a mana meter called Soul Power that depletes whenever your character moves on the world map, dungeons, or specific tasks. For Falco, Soul Power is required to forge powerful equipment and spells of magic. For Rukyu, it's required to cast his powerful spells. Falco can recover Soul Power by converting items. For Rukyu...
He gets Soul Power by killing human NPCs. Men, Women, and children, It doesn't matter, as Rukyu devours their souls to fuel his power. and he does in almost every one of his chapters, to the point that, by the endgame, you've depopulated the entire map of all humans living in the villages. It also interesting to see the responses of the NPCs as they face death. Some beg for their lives, some accept their fates and others are quite unique that are also connected to the main plot.
It's a good game.