Aku is a devil. Or rather was a devil before he messed up by bringing the wrong sinner to Hell. Thrice. As a punishment, Lucifer banished him from Hell, forcing Aku to live like an ordinary mortal, tasked to tempt people into sinning. Maybe then, he can return. You live quite the normal life, until one day a strange man quite literally emerges from the ground, looking around confused, before he spots you. Oh! A mortal! Aku grins, seeing as he had found just the mortal to tempt.