"And if nobody says they're the Demon Lord, a couple of foreigners live happily ever after in our world?  Because that absolutely sounds like an outcome we should be trying for, if there's any way we can possibly try to..."  This is a terrifically good explanation for why you shouldn't tell the foreigners that they have the option of being a Demon Lord.

"And if nobody says they're the Demon Lord, a couple of foreigners live happily ever after in our world?  Because that absolutely sounds like an outcome we should be trying for, if there's any way we can possibly try to..."  Haroun trails off.  This is admittedly a terrifically good explanation for why you shouldn't tell the foreigners that they have the option of being a Demon Lord.