I Thought I Had Reincarnated in a Musou Game, But It Turns Out This Is a Hardcore Grimdark Game

Imagine being reincarnated into the world of a game, without any knowledge of its original story. In a world where the power of demons grew stronger after the death of the hero, one rogue ignored the original storyline and became obsessed with hunting demons. This obsession spelled their doom. The protagonist (originally a man) had one goal: “Skill Development.” For this purpose, demon cores, the demons’ weak points, provided the best nourishment. So why hesitate to kill demons who prey on humans?