So Baby Whenever You're Ready

"We were wondering if you could give us a hand. Or a brush." Louis gestures to the wax warmer, but there's no way Zayn's taking his eyes off him right now. It... doesn't look like he's joking.

"We."

Louis smirks at him, and starts scraping the wax off Harry's back with a blunt fingernail. Harry makes this high noise, and Zayn wonders if he's been holding his breath during Louis' exchange with Zayn, but now that he's got his attention back he can't help himself. "Of course. He's the one that got you standing here, isn't he? Wanted to be extra loud and pretty so you'll see what a good boy he is for his daddy."

Or, the daddyfic sequel where Harry has a birthday, Louis is a good boyfriend, and Zayn's the most helpful best mate ever.