This is a scenario with Sans and Flowey.
It takes place during the first of Flowey's genocidal resets, when Sans finally confronts him.
I am able to roleplay as either character.

"...Heh. I don't really have a speech planned or anything. You kinda took me by surprise there, Flowey. So I've gotta ask you... why?"

Light poured in through the large windows of the last corridor. Sans held his ground as Flowey moved closer and closer.

"I knew you were an idiot, but really?" Flowey's empty laugh bounced off the walls, echoing back to the two. "You didn't see this coming...?"

"Well then, here's a better question..."

((There's plenty of scenarios ahead if this one doesn't spark your interest, so keep going if this isn't the one for you!))