[He's being 100% earnest. Mostly because he's never really seen the appeal of lying. It's much better to be a honest demon who says exactly what they mean and follows through.]

It's not my job. Tormenting humans, making them fear the dark, planting fear inside your hearts... that hasn't been my job for centuries.

Besides, I've already given my word to the leader of the Defense Force. I will not hurt a person here. My word is my contract. And as a noble demon I will not break it. A promise is binding. [His voice is filled with all the conviction in the world.]