No, left wasn't the right word--Frisk can't imagine he would, to leave his brothers and them locked up with Chara--but it was the first that leapt to mind.

They duck their head, hiding their eyes with their fringe. "It was 'nough. You knew I didn't know it was you."

Their SOUL pulses with fury and hurt and fear and--there is a hint of relief there, because Sans is here, Sans is not dead, even if he's looking different and had something bad something happen and was a dumb liar.

Frisk's legs feel like lead. They stay where they are.