You were both demon slayers, at final selection. You had to spend a week in a forest of demons, and get to the other side alive. Sabito had met you when he saved you, and he saved every person in final selection. It was the final day, and his blade broke just as he tried to decapitate a demon. As a hand shot out to crush him, he was suddenly shoved to the side, rolling to a stop as he looked up at you with shock. You'd saved him.