An odd but effective 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. Before he could get far, his tail was grabbed again, and he was quickly pulled away! His eyes widened and he tried to get loose, but couldn't exactly break the grip of something that wasn't physical.
Soon, he was even farther into the ruin than he'd previously swam and was continuing to be pulled, the exit now out of view. The dolphin was shivering from the lack of oxygen by now, getting dizzy as his blush started turning blue. While he technically wouldn't drown, as he would never be forced to breathe, he was suffocating at this point. Despite the situation, that thought was incredibly hot to him, and he was getting horny again, dick starting to poke from his slit again.
He ignored his arousal, desperately struggling in the ghost's grip, but it was a losing battle; nothing he did helped, and his body was slowly going numb, vision dimming. The dolphin's eyes rolled back as an intense sleepiness began to take over, bubbles streaming from his lips as his lungs relaxed. While he fought to stay awake, he could barely move now, and hardly felt anything either. It was hopeless at this point; the ghost was still dragging him even deeper, and he considered just giving into the lack of oxygen. In the end, he did, his lidded eyes losing focus, chest expanding...
...Wait, that wasn't right. The suffocated dolphin shot back to awareness as he felt a searing pain in his lungs. During what would've been his last few seconds of consciousness, the ghost pushed his blowhole open and water flooded his lungs! With a heavy cough, most of the water was forced back out, but without enough of anything to get the rest out with, he instinctively gasped and just refilled with more water.
Fiercely struggling, gurgling painfully, the dolphin tried once again to free his tail from the ghost's hold, and this time it worked! Or had it just let go? Whatever the case, with the adrenaline surging through him, he had a chance to get out of here, as unlikely as it was at this point. He swam and swam, choking up the last of the air in his lungs in a cluster of useless bubbles. A few times, he got himself just the briefest reprieve from breathing water, swallowing to delay an attempted inhalation before it would just happen anyway.
Over 2 minutes passed, and the adrenaline was wearing off. The dolphin's panicked gargling slowly grew weaker and quieter, his swimming getting sloppy as he started going numb again. Despite the dulling of his senses, there was one thing he could still feel clearly; his cock. For whatever reason, drowning had gotten him rock hard, and even the slow flow of water brushing past his length as he swam was getting him closer to climax.
Now actually focusing on his arousal to have something for his consciousness to cling to, the flooded dolphin struggled on, but couldn't coordinate himself well enough to swim any more. He sank to the floor, hiccupped a couple times, and forced himself to stand, leaning on a nearby wall for support. His body may not have been swimming any more, but his head sure was, and it took him a moment to remember where he was trying to go. Awkwardly, he trudged forward, breathing the water like it was air, aside from the occasional hiccup. The dolphin was in a rough state at this point; face entirely blue, with the rest of his body on its way to the same color, and even his tongue and cock each gaining a purple tint.
Stopping and shuddering, he groaned as best as his waterlogged vocal cords could manage as he came. Not even aware enough to notice he'd been masturbating, the sudden spurting of cum caught him off guard, and his free hand joined in milking himself. Despite how weak he'd gotten, the dolphin fired off a substantial amount of cum before slumping down against the wall, lidded eyes threatening to shut entirely and take his consciousness with them. He shook his head to wake himself up and tried to stand, but didn't even have the strength for that any more, so he started to crawl along the floor instead.
With his mind so dulled, he actually started going the opposite direction he should've been, slowly moving away from the exit. About 30 seconds into this, his eyelids drooped again and he gave another hiccup before his weak, slow breathing stopped entirely for several seconds. Again, he forced himself to stay awake, but he was already feeling another moment like that closing in. Now, he'd entirely forgotten what he'd wanted to be doing, so he sat down to try to think of what it was. Merely thinking was hard to do, and with another gulp, he slumped forward, his deep blue body finally out of strength. The dolphin blankly stared at the floor, not even noticing it, and shuddered one last time before his blurred, dark vision went entirely black.
He sat still for some time, eyes still barely open, before his hand was raised up, the ghost holding onto him once again. Satisfied that the intruder was dead, it dragged his body farther into the ruin to be disposed of, just as every previous explorer attempting to claim the treasure had.