Don't sleep on 'Arifureta: From Commonplace to World's Strongest'. The isekai hook is a whole class being summoned, but the protagonist, Hajime, gets betrayed and left for dead in a dungeon's depths. His reincarnation isn't into a new body, but a brutal transformation within the world itself. The harem builds from him rescuing or meeting powerful, often ostracized women who bond with him over their shared monstrous natures. The core appeal is the edgy, overpowered crafting and revenge power fantasy, with relationships forged in extreme adversity.