Sans has no idea what Papyrus can do, yet. Not besides some kind of sleep related magic, which much have a more cohesive theme, because sleeping sure as hell doesn't seem like what his Spark would be based around. Unless it was a passionate hatred.

Sans spreads his wings, steeling himself. His aura thickens, projecting inner strength to the outside, getting ready for when an attack inevitably happens. He knows it's coming but he doesn't know in what form it will be. He can't guarantee he'll be able to dodge it.

The weight of angelic judgement fills the air as Sans holds himself aloft, looking at Papyrus, visibly heartbroken.

"Please don't do this," he says quietly.