By the time the water gets warmer, Remus and Sirius have run out of food and have taken to drifting places in semi-hibernation mode to conserve energy, they even shake their tail scales flat to retain more heat. It's a common thing but this far up in the water, they really shouldn't have to.
They travelled a lot before and the whole reason they made the huge shift to higher places is to not only escape Sirius' large family pod but also for more food. They do get more food of course, they gorged themselves when they got up here, but they also move around a lot more and it seems to be cancelling out.
Remus makes a weaved bag, quite large to take back whatever James is going to get them, and they make the trek over to the reef.
They get to the sloping shelf and guards meet them, a red haired and red tailed Mermaid with familiar eyes.
"You must be Harry's mum," Sirius says but he's looking around for Harry rather than focused on her.
Harry isn't here, neither is James, which makes sense. If Sirius got his mate and kid stolen, he'd never let them leave the nest again.
"There is only one meal for you, you will not get anything else," the Mer -Lily- says firmly, back curled, tail ready to launch into a fight as she's backed up by seven other Mer.
"As long as it's big," Remus says peaceably as his eyes scan the guards cautiously.
Lily purses her lips and nods to the side. "Out by the rock shelf coral, its marked. You leave immediately after and never return." Lily hesitates. "It's not sickness, just - the colour is from not eating."
Sirius flashes a grin full of sharp teeth. "Pleasure doing business with you. You tell Harry I said hi, yeah?"
Remus grabs Sirius' upper arm and drags him off to the side, skirting around the reef with a wide berth until they get to the general area Lily indicated. It's lots of large rocks and partly down a short rock cliff with crevices inside.
"You think they got tuna or something?" Sirius asks in excitement.
"Don't move so much, they look twitchy," Remus mutters, still keeping an eye on the Mers who followed them around, standing far away but watching closely.
"Found it!" Sirius cries and ducks down, seeing a large X marked into a boulder that's almost entirely blocking a crevice. It looks deep at least so it might be really big.
Remus flips over so his tail is out of the way while he grabs the boulder and the rock face with a hand each, pushing the makeshift door open. Sirius waits at the entrance, ready to catch something if it runs.
It's a Merman with a bleached tail, still faintly brown with patches of spots, lying with his ripped tail fin against the boulder and hunched in on himself deeper into the cave. His wounds haven't closed properly, scales shedding down the gash over one hip.
James' eyes flutter open. He sees them and doesn't even look surprised.
Sirius pauses and then just smiles. "What a nice surprise." He grabs for Remus' net wrapped around his arm and swims into the small cave, making it a tight fit with both of them. Sirius holds up the seaweed for James. "Here, come on."
James just closes his eyes again.
Sirius brushes James' hair, longer now, away from his face. "Are you that weak or have you given up?"
The Mer pod here is already large, and when one comes home, injured and crippled and requiring much more food to heal up, then it's just pragmatism to let that one go.
Or feed him to Sirens.
"You think we can get a discount because your tail is bleached?" Sirius jokes, nudging James gently.
James doesn't respond.
Sirius sighs and pushes his hands under James, lifting him easily with the buoyancy of the water. "Remus, you grab his tail."
They slowly manoeuvre the Mer out and James stays limp. He might have actually passed out.
"There's Harry," Remus says as he peeks back over to the reef and sees Harry being held back by Lily.
"You think he knows about his dad?" Sirius muses.
"He would have come to rescue James," Remus points out.
"You wanna show him so he'll follow us?" Sirius smirks.
Remus huffs a bit but gathers James into his arms so he can swim with him. "Let's go."
Sirius lingers to the side as Remus swims off with James, in full view of Harry, who stares after them in shock. An argument starts up behind them.
The two Sirens pause just off the shelf and they readjust James with the netting wrapped around him to make it easier to carry him properly. They wait a bit more and Harry comes streaking over the side only to double back quickly once he catches sight of them.
"Is there some kind of medicine you Mer need or…?" Sirius trails off as they start to swim again.
Harry flutters worriedly around Remus and his cargo. This close up, Harry has grown incredibly big, almost two metres now. "I – well, dad was getting better, he was eating all the food I sent him."
"Does it look like he was getting food?" Remus asks kindly.
Harry looks up at Remus, looks down at James, looks up again. "But…"
"You're a bit sheltered," Sirius reassures Harry. "Don't worry, we'll get your dad back and he'll eat his way through the entire forest and get better again."
Harry needs to chew up the seaweed at first, but James slowly recovers enough to slowly swim around through the trench for exercise.
Remus usually stays in the nest with James while a much more energetic Harry -who has gotten even faster since they last saw him- herds fish towards Sirius when they hunt, bringing back enough food for the Sirens as well.
"I didn't eat as much food because I wasn't doing as much work, I made that decision by myself," James admits to Remus one day while Harry and Sirius are out. "And then, I guess with the injuries I started bleaching and they said I was sick so…I went into…isolation."
"You agreed?" Remus asks with a frown, floating upright like James as he holds onto the other side of the rusted, giant ship anchor, the thick chain trailing off into the seaweed surrounding them.
"I knew you were coming," James says quietly. "Lily and I talked. They would have kicked me out if I refused, and I know Harry would have tried to fight but I - I can't do anything like this." James gestures vaguely at his ruined tail. "I knew you were coming."
"We followed you when you went home," Remus says. "You left us in the sand, I was ready to quit a couple hours in."
James' eyes flicker up to Remus and he starts to smile. "Yeah?"
"I've seen those other Mer swim, I'm surprised you didn't just take your guard job as soon as you got back," Remus insists.
"With my tail, I didn't even try," James explains.
"A waste," Remus tsks.
James laughs and flicks his tail happily, still bleached but a soft gentle sort of brown and it still glimmers in the faint sunlight reaching this far down.
Nights pass.
The water turns warmer and then starts to cool again.
Harry never mentions going back to the reef.
Neither does James.
Remus swims back through the seaweed forest, pausing at a little bald patch in the sand with a frown because Harry keeps taking from the same area even though Remus has explained why he shouldn't.
Remus reminds himself to transplant some more and continues on his way, the long seaweed swaying with the current and blowing back where he swims past and the water pushes at it.
Harry is almost fully grown now, still cuddling up to James as they sleep peacefully in a nicely decorated nest. James' tail has almost completely shed back to a lovely warm brown with streaks of highlights and his usual little clusters of white spots. Sirius is half on top of the Mers, longer tail wrapped around theirs.
"Get up!" Remus calls, slapping at them gently with his tail. "You've slept in long enough, come on, the fish will all be gone by the time we start hunting."
"I'll catch them," Harry mumbles in his sleep. "Hmmm 'm fast."
James makes a clicking coo noise and Harry settles back in.
Sirius gets startled awake because that's not a Siren sound and his instincts shake him alert. He blinks and looks around before flopping back down. "Ugh, what have I said about Mer noises?" he complains.
James purrls and then hums, leading into a sort of whistle.
Harry makes a happy noise.
"What does that mean?" Remus asks, floating closer in curiosity.
"Safe," James sighs in contentment. "Protected."
"I don't know, I'm feeling kind of hungry," Sirius says and snaps his teeth at James.
"I would destroy you," James says, still half asleep but far too confident.
Harry reaches up and pats James' head. "Don't bully him."
Sirius looks at Remus in outrage. "You're just going to float there while our kid talks shit about me?"
"Harry, don't talk to your Sirius like that," Remus huffs in amusement and hits Sirius again with his tail. "Get up, we need to head out."
As stationary reef Mers, and as the previous foremost guard and hunter, James knows a lot more about migratory patterns of fish nearby and he can schedule things with an error of maybe two days. It means they get more regular food but they need to work around the patterns.
Harry goes on most hunts because of how fast and agile he is but he deserves a break too. Sirius still clearly thinks about making Harry do it but huffs and pushes off the sand, floating up and shaking himself out, tail once more shivering into slightly raised, razor sharp scales that he had flattened out to sleep with the Mers.
"We'll be back soon, okay?" Remus tells the Mers. "Call if a predator comes close."
James scoffs. As if they didn't watch James take down that Siren that had followed Harry back to the trench one day. They only saw the second half of that fight too because James had already beat it into submission by the time they showed up.
"Call," Remus says firmly.
"We will," Harry says obediently. "Have fun."