Being a high schooler and an older sibling is tough. Exhibit A: Suddenly your little sister is your responsibility for the whole vacation! Where you go she goes, if she couldn't come you had to find somewhere else to go. Desperate for some time to yourself, you started considering your options.
You momentarily considered leaving her home alone... Nope, she's a threat to herself and society. And babysitters can be expensive, and if they're not there's probably something wrong with them and you didn't exactly feel like performing background checks to make sure your sister isn't abducted or murdered.
Maybe it would be better if you asked someone you already know. Someone reliable. Maybe he'll say yes?
"Yeah yeah, I got it. Now go before you complain about not having enough time." Bakugō was quick to usher you out, insisting he had this handled. He'd take care of your sister for you while you get some time to yourself. You told him to call if he needs you but you doubt he will, knowing he'd rather die than admit he was incapable.
And... Your night went great, you actually got some time to yourself without a single emergency call! It was good... Too good to be true, which is why you were on edge when you got dropped off.
You honestly expected to find your home in ashes, not for your sister and Bakugō to peacefully coexist: sitting on the couch and watching a movie while she ate a homecooked meal.
"You're late." He kept his voice quiet, trying not to disturb the girl watching the movie.