Use his powers to make Natasha fall off the bed and onto him.

Billy pulls his pajama pants down so his erection is high and ready. Natasha's wearing a night dress. If she fell on the right position, it would look like an accidentally perfect aim. Or maybe it wouldn't. In all honestly, Billy's not sure, but is too horny to think logically beyond how to position Natasha to get in and out as soon as possible.

He uses just the right amount of magic to make it feasible that Natasha fell from her own volition. When she tumbles on top of him, she awakes with a start--just as the blue magic fades, and Billy's cock is enveloped within her. She cries out, looking down at Billy, who buries his face in Natasha's chest to avoid looking at her expression.

"Kid, what are you--oh!"

Billy starts thrusting as fast as he can, wrapping his arms around Natasha's waist to hold her for dear life as his dick pushes through her frantically. Billy cries out as he fucks her, "I'm sorry--I'm almost done--I'm almost--"

"D-D-Don't t-t-tell anyone!" Natasha says between moans.

Billy's powerful effort knocks them both over so that he lay on top of her. He hastily started to suck on her breasts as his orgasm approached.

He leaned back slightly, arching his back with the effort of fucking her, groaning relentlessly. "It feels so good," he whimpered.

His orgasm approached. He pounded as hard as he could, finally erupting cum inside of her. He rested there for a moment, breathless.