Alright, right now you have two priorities-
1: Locate Noriaki Kakyoin, and rescue him if he's still alive.
2: Murder that rat bastard that calls himself Tennile.
Step 1 is going to be tricky, but step 2 is easy. Aside from simply ganging up on him, if you swap his lungful of air (which will supposedly last him 7 minutes) with your lungs full of co2, he won't realize he's drowning until he passes out. The only tricky part is touching him.
You send Uno up to the surface and Cinque up behind her to complete the chain. Due, meanwhile, bounces back and forth to each of your allies and then the sailors, swapping their held breath with fresh air. Flashdance can't speak, so you can't tell them not to exhale, but surely that's obvious enough advice that they won't need to hear it?
Doing a round trip around everyone and then back to yourself only takes Due a second or two, and Joseph even nods to her as if he understands what's going on. With that, you turn to refocus your attention on where you last heard Tennille, but before your can even focus on where he was, his Dark Blue Moon has surged past you and crashed into Jotaro with torpedo speed. The shockwave of their first collision is forceful enough to send you tumbling head-over heels in the water, losing track of which way is up.
You hear a muffled "ora ora" as Star Platinum rains down its freakishly powerful blows against Dark Blue Moon, but when you gain your bearings enough to spot them again through Quattro's eyes, the fight isn't going quite how you hoped. Star Platinum's knuckles are covered in barnacles, and deep slashes run along its powerful arms, the marks of Blue Moon's vicious claws.
"Hahaha!" rings Tennille's voice from his Stand's unmoving mouth, "where's all that arrogance now, scum!?"
Faster than your eyes can properly track, Dark Blue Moon swims above and around Star Platinum, appearing behind Jotaro to attack him in the flesh. Before its claws can close in, though, Star Platinum's elbow meets its round face, sending it surging backwards with a trickle of blood.
"You've got more than enough for both of us, jackass."
You can't pay attention to that. Sending a Flashdance into that melee would basically be suicide, even for Quattro. So the best move has to be to look for Kakyoin, right?
You don't spend too long thinking about it, sending Due 7 meters deeper and then swapping with her, then doing the same with Tre, leaving yourself at basically the end of your chain, with only Quattro for protection. Down here it's nearly pitch black, and the salt water stinging your eyes makes looking even harder. You notice unexplained pain you didn't have before and notice single barnacles digging into you, no major threat for the moment, but a major danger of growing. You need to hurry.
Through Cinque's eyes, you see the fight between Jotaro and Dark Blue Moon going poorly- obviously, fighting underwater is slowing Star Platinum down, while Tennille is growing in strength every second.
You refill your lungs and redouble your efforts to find Kakyoin. At last, through the tiny bit of light that filters this deep at night, your eyes manage to pick out a trickle of red in the inky darkness. Swimming after that ghost of a red current, a dark shape in the water finally emerges, forms into a silhouette, and takes the shape of a bloody and unmoving Noriaki Kakyoin. You swim over and note one grievous wound after another. A terrible claw mark, like four sword slashes, travels from his left shoulder to right him. His right arm, too, is broken and mangled. He's got barnacles all over as well, though thankfully not yet nearly enough to fully cover him.
Your first thought is that he must be dead, but when you get close enough, you can make out the wispy-green form of Hierophant Green wrapping around his wounds, slowing his bleeding and proving his soul is still in his body. Quattro reaches out to fill his lungs with air, but it's too late- in his unconsciousness, he's inhaled gallons of seawater, which you can't swap for the much less dense air. His only hope is getting to the surface.
Since Uno up top has no human-shaped object to swap with Kakyoin, you have no choice but to swim him up. Quattro refills your lungs one last time, takes hold of some parts of his body free of barnacles, and begins forcing him up through the water. Just below them, you begin swimming up too.
You're 24 meters below the surface. Once you reach 7 meters down, Quattro can swap with you to leave you with Kakyoin so you can get the water out of his lungs and leave him safe on some debris. That 17 meter swim will take you 25 seconds.
During the length of that 25 seconds, through Cinque's eyes, you watch a cataclysm.
The fight between Star Platinum and Dark Blue Moon is still going poorly when you check back in. Each successful punch leaves more barnacles on Star Platinum's fists, which all at once hurt, cause more blood loss, and increase the water resistance on Star Platinum's fists, slowing him down yet further. Jotaro has gone nearly a minute without air, so that can't be helping either.
Meanwhile, each drop of its enemies' blood that Dark Blue Moon inhales sends it into a greater frenzy, its speed and strength increasing further. If Star Platinum didn't possess such godlike power normally, it would already be fish food, but as is, Jotaro is just barely able to hold out and protect his physical body.
Meanwhile, Polnareff and Joseph are swimming closer to join the fight. Joseph is faster, and reaches out with Hermit Purple to entangle Dark Blue Moon, but is instantly rebuffed- the moment his Stand makes contact with Tennille's, its razor-sharp fins and scales cut deep into the vines, like trying to capture a sword with knitting thread.
Speaking of swords, though, Polnareff's Silver Chariot joins the battle soon afterwards, and it has a bit more luck. Its thin blade glides through the water with much greater ease than Star Platinum's fists, and Dark Blue Moon is forced to back up a bit as that flashing rapier cuts thin slices through its back and arms. Swiftly, though, it focuses on this new foe, and at that point, Polnareff's hope for a swift victory is immediately dashed.
The knight drives its blade down into Dark Blue Moon's chest, but it's blocked by a sudden growth of barnacles on the body of the aquatic Stand, and Blue Moon acts quickly, smashing the blade of the sword with such force that it's torn out of Chariot's hand. Suddenly woefully unequipped for this "sword fight," Chariot tries to dodge back, but is pounced upon by Blue Moon. Thankfully, the sharklike Stand seems to have a bit more trouble tearing through Chariot's metal form than it does flesh, but not much.
Avdol, meanwhile, watches with the furious expression on his face matched only by that on his Magician's Red. It seems he can't attack at the moment, and you can guess why- the flames of his Stand underwater either don't work, or will boil the water and turn his friends into lobsters. Distantly, you hope it's the latter and that Magician's Red will at least work as a last resort.
As Dark Blue Moon is distracted with Polnareff, Star Platinum grabs its ankle and drags it back into their fight, preparing what looks like a monstrous punch, but it falters as blood surges from its hand, sliced by the fins on Blue Moon's ankle. The punch still lands, but with less brutal force than you'd been hoping. Still, it seems to manage to make Dark Blue Moon at least temporarily retreat, slinking back into the darkness.
Its disappearance is momentary, though. As you spot moonlight above the waves, the Stand reemerges with terrible speed, tearing right through one of the sailors. As the others let out silent, gargled screams full of the last air in their lungs, Blue Moon slashes through them, chopping out pieces like a rampaging animal, inhaling their blood as it flows out into the water. Having swam closer to Jotaro, all your allies are too far to help, and one by one, the sailors are torn to shreds.
Blood blooms from their dismembered corpses, creating such a great red cloud that you completely lose sight of first Dark Blue Moon, then Polnareff, Joseph, and Jotaro as it continues to spread through the choppy currents.
As this last horrifying development is completed, Quattro finally reaches the surface with Kakyoin, and you swap places with her immediately, hauling Kakyoin onto a piece of floating wood and taking a deep breath of air. His lungs are full of seawater, and though you can't directly transport it out, you have a nice second option. Quattro's hands enter his chest and press gently down on his lungs, compressing them and forcing him to suddenly cough up one breath after another of water.
The shock to his system also sends his body into overdrive, and he suddenly regains consciousness and starts to take desperate inhalations even as with every other breath he vomits up more saltwater.
"Kakyoin!" you cry as soon as he's rolled over onto his unbroken arm and seems relatively lucid. "Look at me! Look at me!"
His eyes snap to you and look unfocused- it's no wonder, he just went without oxygen for about a minute and a half. You only hope he hasn't suffered any permanent damage. "M-Marta?"
"Kakyoin, you're hurt bad. Hierophant is already taking care of you, but stay here! Get as much water as possible out of your lungs, take deep breaths, and if something with fins comes out of the water, blast it before asking questions!"
You take one more breath, and before hearing his response, you dive back under. Swiftly swapping to Cinque, calling Quattro back to you, and then returning the other girls to their original spots, you're relieved that moving underwater is *much* easier when you don't have an unconscious body to drag around.
Unfortunately, what isn't easier is seeing what the hell is going on. The massive bloody blot in the ocean is leaving you- and worse, your allies inside it- completely blinded to Dark Blue Moon's location.
You realize you don't see Avdol anymore. You stopped paying attention for a moment to take care of Kakyoin, so what happened? Did the blood cloud expand to his location? Did he swim into it? Or did he get dragged into it or out into the depths?
You realize you don't have time to worry about this. Even if you didn't care about saving the lives of Jotaro and the others, the fact remains that if they die, you're a sitting duck and basically as good as dead down here. There's only one choice. Ignoring the increasing pain of the barnacles that are again spreading along your arm and now also your torso, you swim into the blood cloud.
Inside, your visibility is limited to five feet at best. Knowing that Dark Blue Moon probably has some ability letting it know where you are, you feel incredibly vulnerable, and have Tre, Quattro, and Due all watching your back as you search through the reddened waters. Suddenly, you feel the water getting much warmer. Suddenly hopeful, you swim in the direction of the increasingly jacuzzi-hot water until you catch sight of Avdol. Reflexively, he holds out Magician's Red's hand, but recognizes you and calms down, though he's obviously struggling from a lack of oxygen. You reach out with Quattro and refill his lungs, nodding and trying to gesture that he'll be OK.
"You've teleported fresh air into my lungs?" he asks through his Stand. You nod an affirmation.
"I still feel like I'm suffocating, but I'll take your word for it. The others must be in a similar state. Come on."
He swims away and you begin to follow, but you don't get far before Cinque screams a warning and almost immediately you're caught by a brutal tearing force. The last thing you see through Cinque's eyes is blue claws tearing her literally in half at the waist. You feel like you swallowed a handfull of razor blades, but that isn't the worst problem. It seems Tennille is dragging Cinque's body into the depths, and since Cinque is between you and Uno in the "chain," that means both of you are being dragged down with her as if tied to her by a leash.
Not only is your "snorkel" cut with Uno pulled below the surface, now you're being pulled deeper and deeper, away from Avdol and the others. As you're dragged down, though, Quattro catches sight of another figure in the dark between you and Cinque- Dark Blue Moon is pulling you right past the fake Tennille! As you're sucked by, Quattro and Tre grab him. He doesn't seem to have been expecting this as the two of you together get pulled past the last of the light, cast into a pitch darkness at the seafloor.
You're blind, but you can still feel the splashes Tennille is making in the water and Quattro strikes for them. You can feel her fingers dig deep into flesh and Tennille lets out a gurgling scream, followed by a terrifying screech from Dark Blue Moon, which is immediately distracted from Cinque's corpse, which it is brutalizing, to charging straight at you.
Just before it reaches you, it goes silent, and you do your best to time your dodge despite the darkness, swapping with Uno just before it makes contact. Its claws dig into her chest and tear up through her breasts and to her shoulder- if she hadn't already been missing her arm, it would certainly have been slashed off now. The water roils in your mouth as you try to resist screaming- it isn't enough.
Your choked off cry of pain alerted Dark Blue Moon to your new location, and it charges you completely silently this time, and when it slashes, it meets flesh. You swap with Uno halfway through the attack, but as you float in the water near Tennille, you can feel that Blue Moon's claws tore your face open completely, ripping from your cheek up to your eyebrow- and, you think, completely gouging out your left eye in the process. The pain is excruciating, nearly as much as the horrible feeling of knowing you're permanently injured is terrifying, but both of those experiences are forced to the back by a terrible blinding rage.
When you attack where you think Tennille is this time, it isn't only with Quattro, Duo, and Tre, you also dive out yourself, your fingers blindly grasping for anything vulnerable, his wounds, his eyes, his balls, or anything you can hurt with your bare hands.
You make contact, albeit not with any of those, but with what seems to be his legs. Dark Blue Moon senses danger and turns around again, tossing aside a ragdolled Uno in the process. The Stand throws you to the seafloor, and though you swap with Tre, you're losing too many of your girls. If if tears her up the way it has Cinque and Uno, you'll be more than halfway torn to pieces, which certainly sounds fatal to you. Due and Quattro try to attack Dark Blue Moon from behind, but if Chariot and Star Platinum couldn't hurt it together, they stand no chance.
As your shoulders begin to crack with the sensation of Dark Blue Moon bodily crushing Tre like an egg, another pain hits you- your already-damaged ears are cracked with a second shockwave traveling through the water, and though your hearing is in terrible shape, you can hear a violent scream of "ORA" along with the shockwave- and you realize that the damage you just took hurt Tennille too, blood spurting from Dark Blue Moon's tiny ear holes.
It seems in its frenzy, Dark Blue Moon focuses on hurting its current prey and takes a moment to react to its master being in danger. In that respect, you and it have something in common. Quattro snaps away from Dark Blue Moon, and aiming for where you estimate Tennille was last time, she throws out a knife-hand strike with all her strength.
"AN EYE FOR AN EYE!" you scream, though it comes out as a bubbling and halfhearted gurgle underwater.
As if guided by the hand of the Devil himself, Quattro's fingers find their mark, stabbing into Tennille's skull and then curling into a fist, dragging out everything important at once.
He dies so quickly that Dark Blue Moon doesn't seem to realize what happened for a moment, writing on top of Tre and crushing her shoulders before it crumples away and fades to nothing, along with all the barnacles covering your body.
The sense of relief sweeping over you is so great that you barely even notice that your cry of rage emptied all the air in your lungs, and as you black out, you barely even care.
For the second time in as many days, you awaken floating on a raft under the beating sun, though this time you somehow feel even worse. Your field of vision is definitively one-sided, and you reach out with a mercifully-numb arm to feel your left eye is wrapped in cloth.
"Sorry," you hear Joseph say, though his voice is muffled through abused eardrums and you haven't got the energy to turn to look at him, "it was basically torn right out. Short of supernatural healing powers, you'll… have to start getting used to no binocular vision. I'm… sorry I brought all of you into this."
"No. You didn't bring me into shit. This… all this… my fucking eye.." You feel yourself tearing up with impotent rage as you grip the bandages around your eye. "It's DIO… DIO brought us into this. All of us!"
You sit up, though the experience is a miserable one. At least you're not concussed this time. Due appears and opens her eyes, confirming what you already thought- both of her eyes are fine, and you can see through them without issue. You're different from other Stand-users. Damage to your Stand reflects to you in fifths, but not vise-versa.
"Joseph, you said Hamon hurts vampires, right? You're going to teach me Sendo, and I'm going to rip out DIO's fucking heart."
You hear movement from across the piece of wrecked ship you're all sitting on, and turn to see Polnareff. "A technique that can hurt vampires, monsieur Joestar? If you can teach something like that, then I think Marta has the right idea. Teach me too."
Joseph smiles bitterly. "I can't promise I'm a good teacher. But you're right. We can't afford to not use every advantage that we have. We'll start right away."
Sorry for the long break! This chapter's already long enough, so we'll continue with another update (this time with an actual choice for you guys) in a few days! Also expect the chapterly update with everybody's status then too- for now, the summary version is "fucked up," especially Marta and Kakyoin.