>>281784854
Just saying there's no way for her to explain it properly when it involves concepts that don't even exist. Especially to a guy who's not exactly the brightest bulb in Denji (the dude just completely ignored several explanations from Death, Miri, Fumiko, etc.).
All Asa definitely knows it's really, really bad.
Worse than extinction though? Eh, not really, based on what we know so far. As long as people exist, there's always a chance to fight back, which seemed to be Denji's stance on the matter. Deal with the potential apocalyptic event first, then worry about the rest.
However, he probably expected Death Devil to be some gigantic monstrous freak like Nayuta had built it up to be, instead of a cute girl he already knew.