You bump into the belly of a large male orca. You swim around its side, and take a large gulp of air as you surface. The orca's face is right next to you, and you can see him eye you greedily. You are surprised to hear him speak, "Human, you have entered my domain, and you will do what I ask or you will never leave."
It seems you have no choice but to obey. You stutter, "O-okay, I suppose I have to."
"Good, then let's start." The orca says with a hint of a chuckle. He swims around behind you, and shimmies closer to you. You go underwater, the orca's belly on your back. You feel something hard rubbing at your thighs. It moves closer to your ass, and presses lightly. You realize he is going to fuck you, and you can't stop him. The orca rolls on his side to give you air, and as he does, his massive cock slips between your cheeks. The head of his cock presses lightly at your anus, and you feel a wave of pleasure go through your body. You suddenly want this, you want it badly. You lower your ass onto his cock a fraction of an inch, and already you can feel it stretching. His huge penis must be three or four inches wide. He presses deeper into you, and you can feel your first sphincter give way. Your own cock is throbbing madly. The orca is being very gentle with you. He rests the tip of his cock at your second sphincter for a moment before pressing a bit more. Waves of pleasure course through your body as he slowly pushes into your rectum. The massive cock is stretching you, but the orca is being so gentle it doesn't hurt. The tip of his cock reaches the end of your rectum and pulls back. He pulls all the way out, and re-enters. This alone brings you to the brink of orgasm. He pulls out once more, gradually increasing speed. He thrusts again, and your body tenses as you orgasm, harder than you ever have before. His cock throbs as he ejaculates into your colon, letting out gallons of semen into your intestines. It feels wonderful. So wonderful you don't want the orca to let you go. As he tries to pull out, you clench your pelvic muscles, holding him inside you.
You say, "Please, it feels so good, leave it inside." The orca obeys, and lazily rolls on his back. You lay on his belly, consumed in pure ecstasy. The orca rolls back onto his side, and swims over to the shallows. You slowly drift off to sleep, the orca's mammoth cock still inside you.