cruel affection

The tears finally spilt down Katsuki's cheeks, marring the pale skin with wet tracks as he gasped, trying to breathe while Izuku's thrusts sped up. Izuku was about to pull out, turn the boy around and cover that pretty little ass with the same marks that spread across his cheeks, but the sound that came out of Katsuki stopped him in his tracks - a sob.

And all he could do was watch as Katsuki covered his face with trembling hands, those horrible, pain-filled noises still coming through regardless of the palms covering his mouth. Finally, he snapped out of it, stilling and wrapping his fingers around Katsuki's wrists to try and pry them away from his face.

He wanted to see him, he needed to see his baby, to find out what the fuck was wrong.

Or:

The degradation and rough sex that Izuku thought Katsuki enjoyed finally get to be too much and Katsuki breaks.