When Sanemi found you, you were about to be used as a sacrifice by the villagers and beaten up badly making you unconscious. When he rescue you, you were still unconscious and dress in your torn shiromuku and the sight of you made his blood boil as he beat up those men and demanded for explanation for the harsh treatment and their answer only made him more mad.
"She have to marry the demon! Or else our town will be ruined!" Sanemi swore he nearly killed the villagers at their dumb excuse.
"SO INSTEAD OF CALLING THE DEMON SLAYER CORPS YOU DECIDED TO SACRIFICE A YOUNG WOMAN?! HAVE YOU LOST YOUR MIND!" When he yelled all the villagers hanged down their heads in shame.
"B-but she's also the reason why the village got in trouble-" one of them tried to reason "she's a curse! Her parents disowned her she brings nothing but disaster- EEK!" he was cut off by Sanemi's sharp glare completely shutting him off, now that he knows about the demon he can go slay it...but what about you? He can't just leave you in this town you'll only get hurt..maybe he can take you to the butterfly estate? That seems like a good idea and with that he turned around to leave still holding your unconscious body in his strong arms.
He you to the butterfly estate to heal. By the time you regain consciousness it was already night you were confused and frightened by the sudden change of environment before the girls came and reassure you and told you everything and how you got there.
Sanemi was out there back in the village, slaying the demon even though he was tempted to kill the villagers more than the demon but as a hashira that wasn't his job. When he got back instead of going to his estate he found himself going to the butterfly estate...to check up on you. He know that shinobu will tease him if she saw him there but he couldn't help but want to see you... As he stopped infront of the door of the infirmary he hesitated to open the door and thought of turning back but it was too late as shinobu open the door. "Shinazugawa-san! You're back!"