An odd guardian

This was the place; an ancient temple of some kind, on the shore of the ocean, having been flooded long ago by the very slowly rising sea level. The intrepid anthro dolphin set his supplies next to the entrance, undressing before pulling on his swim trunks and beginning to wade into the water. Supposedly, this place still held treasure even after all this time, just waiting for someone like him to take it.
Now swimming above a staircase that descended underwater, air rushed in and out of the dolphin's blowhole as he surveyed the depths; the path ahead was clear, and lit by an interesting bioluminescent algae. The light was certainly welcome, though he didn't need it, being capable of echolocation. As he started to grow lightheaded from panting, the dolphin took one more deep breath, filled his cheeks with a little extra air, and firmly shut his blowhole as he went entirely underwater, swimming along the passage.
The hall soon became wider and taller, maybe about 15 feet wide and 18 tall. It was still a bit disconcerting, swimming with a ceiling above, but the dolphin focused and tried to put his fear aside, knowing he had plenty of time. There were a few fish around, going about whatever lives they had in this place and paying him no mind, even when he got close. It was a good sign; there likely hadn't any sort of predators here in a long time.
Another few minutes of swimming along and checking out each side area, and the water grew a bit chilly as he continued, though not enough to be an issue. Something in one of the side paths caught his attention with a slight shine... Treasure! Eagerly, the dolphin swam over for a better look, finding a pile of gold coins, which he scooped up as many of as he could. While he hadn't brought his waterproof bag down here, he could still carry a few coins in his hands, and went back into the main hall to bring them back to the entrance.
This time, though, things seemed different. The chill got slightly more intense, and the fish darted off to various side areas as the dolphin approached. There didn't seem to be any issue, scanning the area both visually and with echolocation didn't let him find anything out of what seemed to be the ordinary. Still, he was getting a little nervous again, and was feeling the need to breathe as well, so he picked up the pace a bit.
Something brushed against his tail, and he whipped around to see what it was, a few bubbles leaking from his lips from being startled. Again, though, there was nothing... Trying to convince himself he'd imagined it, the dolphin just kept going, faster again. As he neared the surface, however, something grabbed his tail, keeping him from moving! He yelped out bubbles and reflexively swatted at... Nothing. There was nothing there, but his tail was being held regardless.
As the panicking dolphin pulled and pulled at his tail, he began feeling the sensation of being rubbed in several places, almost in a sort of attempted comforting. With even echolocation still revealing nothing, he paused for a moment as he realized this force that was handling him was a ghost! Just after he realized that, it seemed to shift its focus, tugging on his swim trunks and starting to pull them down. The dolphin tried to stop that from happening, but the ghost held his hands back, and no sooner had his crotch been revealed than the rubbing sensation began along his slit.
His struggles slowing to a stop and his panic turning to confusion, the dolphin's tail was released as he started to get aroused. He looked over at the surface, only about 20 feet away... He didn't need air that badly, he could relax and let this strange spirit take care of him. Besides, he enjoyed the growing strain of holding his breath for so long. As he came to the decision to stay for a while, he closed his eyes and relaxed, the ghost holding him off the floor with force that felt like he was laying on an exceptionally soft bed.
It seemed to know exactly what he liked; as it masturbated him, it would occasionally squeeze his tail a bit or gently rub the skin of his blowhole. It was definitely reading the dolphin's mind, and while he wasn't a fan of that concept, he didn't mind it being used for something like this. The ghost was doing such a good job that, with his eyes closed, he briefly forgot he was underwater, thinking he was just holding his breath during regular sex, as he enjoyed.
With an unexpectedly bubbly moan of pleasure, the dolphin remembered both where he was and just how long he'd been holding his breath. His lungs were burning a little at this point, and he glanced at the surface again before looking back at his cock, a subtle deformation moving along it being the only visible sign of his spectral lover. He could stay a bit longer, at least until he had an orgasm, which wasn't too far off at this point.
Starting to get lightheaded, he let some stale bubbles loose from his blowhole as his arousal passed the point of no return. With a strained smile, the dolphin held back his orgasm to make it stronger, bucking his hips as the ghost's movements sped up. Finally, he let go, cum immediately shooting free of his cock as he moaned again. Just over a dozen more shots followed, most being paired with some bubbling from his mouth, blowhole, or both. Even as his orgasm tapered off, the spirit continued to pleasure him, milking out a few more spurts before he was out.
The distraction wearing off, the dolphin remembered how badly he needed air. With the ghost seeming to be done with him, he whined and took off for the surface, a purple blush on his face. He wasn't stopped this time, and air bursted from his blowhole as he surfaced, gasping heavily. Climbing out of the water, he grabbed his towel and made to dry off... Oh, damn, I forgot my... Something soft landed on his foot. His swim trunks! It seemed the ghost grabbed them for him, and it had also brought up the coins he'd intended on retrieving. The dolphin smiled and put his trunks back on, picked up his waterproof bag, and dove back into the water, eager to bring back the rest of the treasure he'd found.