Make this casual and informal.

Could you please explain why you transformed into a demon? Was it deliberate or against your will? Perhaps it was due to intrusive thoughts? Regardless, I am obligated to eliminate you now.

Hey, can you, like, explain why you turned into a demon? Did you do it on purpose or was it, like, out of your control? Maybe those weird thoughts had something to do with it? Anyway, I gotta take you down now, no hard feelings.

Take out the "like" parts and make slightly formal.

Hey, could you explain why you transformed into a demon? Was it intentional or beyond your control? Maybe intrusive thoughts played a role? Regardless, I'm obliged to eliminate you now.

So, let me break this down for you in a more chill and informal way. First off, dude, I gotta say, transforming into a demon sounds pretty crazy! But I totally get that you want to know how and why it happened. Was it like, a voluntary thing or were you just dragged into demonhood against your will? Maybe it had something to do with those intrusive thoughts, huh? Regardless, now you're telling me you're obliged to get rid of yourself. That's wild, bro!