A/N: Warnings for dub-con. Set when Robin was Slade's apprentice. Another one-shot to follow, potentially. I had an idea but it was weeks ago and I don't remember it anymore. Maybe when I open the word doc that has the beginnings of it written down (well it just has the word butts but still) it'll jog my memory.
"Robin…" Slade said, a note of warning in his voice. The apprentice hesitated but opened his mouth obediently, frowning as his Master didn't plunge right into his throat like usual, but instead traced the tip of his cock around the teen's lips, painting lines of precome that dripped down his chin. Robin swallowed nervously as best as he could with his mouth wide open, and at that moment Slade thrusted his hips forward, burying himself in the unwilling apprentice's mouth. Robin choked a little but quickly suppressed his gag reflex, breathing through his nose as his Master fucked his throat, going from shallow, teasing thrusts to long, deep ones. Robin tried his best to breathe around the ever-growing cock in his airway, relaxing his throat and swallowing the way he knew Slade liked. Confined in his tights, Robin felt his cock get hard as if of its own accord. Robin swallowed again and bobbed his head, hiding his blush, trying to get himself under control. He would not admit to himself that he liked this.
Robin felt hands in his hair, soft without any hair gel that Slade had forbidden. The boy braced himself and, just like he expected, his head was being held still as Slade fucked his throat, Robin's saliva dripping down his chin and onto his Master's balls. Before he knew it, Slade's thrusting stilled and he was coming deep down Robin's throat, pulling out with a cruel grin and letting the last of his come splatter on Robin's face. He spluttered and wiped it off with his hand, getting to his feet carefully in hopes that Slade wouldn't see the hard-on barely concealed by his pants. Robin glared at his Master and then disappeared into the bathroom joined to Slade's bedroom, looking anywhere but his cock as he pulled his tights down and gripped his length, letting Slade's come act as lube as he jacked his dick, hand sliding up and down to give himself the release he craved every time Slade forced him into one of their sessions.
Outside the locked door was Slade, a huge shit-eating grin on his face as he listened to his apprentice's barely-audible gasps and groans through the wall. He waited until he heard the low moan that indicated that Robin's release was at hand when he spoke, a teasing lilt in his voice: "I'm glad you enjoy our little trysts, Robin."
In the bathroom, Robin's eyes were closed, his release at hand, when he heard Slade speak. He made a small squeaking noise and came suddenly, his emissions splattering on the floor. Robin's face flushed beet red and then he heard Slade speak again.
"Clean up and then join me in the gym, we have more training to do."