Harry returned every single Sunday, for which Tom made sure to stay up late waiting. He told himself it was to keep an eye on his enemy, to stare doom in its face so he would never relent searching for a solution. Yet as time passed, it felt like it grounded him to wait for the young merman to arrive. They didn't converse much, the creature now and then pushing words or simple melodies through the glass, which Tom responded to with a few hand gestures he'd learned over the weeks such as 'Thank you', 'Appreciation' or 'Wait'.

It did not appear hostile; asking questions, talking proudly about its catches as if expecting Tom to be impressed or showing lake 'treasures' he'd found in rare flowers or pretty shells. For his part, Tom strategized that it'd be good to show how well he controlled magic, how dangerous he could be, practising all the new charms he was taught during schooldays on those quiet Sunday evenings. Each time, Harry's mouth hung agape.

Sometimes, they merely sized each other up, the creature's somewhat bulging eyes travelling over Tom - his legs in particular. Taking it as a sign that staring was fair game, Tom inspected the long, swaying tail on many occasions. He'd initially thought it to be black and smooth until one night spotting patches of bright scales shimmering through what appeared to be a layer of a dark substance the tails had been caked in for purposes he didn't grasp. The books mentioned nothing of the sort, rather speaking of how merfolk took special pride in their tails and liked showing them off. The brighter, the better to attract a match. As Tom could not convey his questions about it, he remained silent, merely eyeing the patches on nights Harry did not evenly cover the scales.

His peers were of no help in gathering intelligence either, for while he'd gained better standing with his year mates after excellent class performances and being overall well-liked by teachers, no-one would breathe a word about Merfolk to someone who'd brought a curse upon himself that foretold he'd be devoured by the creatures. None wished to get involved and potentially dragged into it themselves.

Thus, he made it his next mission to get into the restricted section, either to find a counter-curse or to get his hands on better books about this elusive species.

Tom's motivations had developed beyond eliminating the threat. He'd grown used to the other's presence and frustrated by his own inability to reach the merman in a similar manner as how Harry spoke through the glass. For better or worse, he needed to understand Harry's reason for showing himself every week.

Pressing a hand to the window, Tom couldn't stop himself from smiling when a webbed one was placed against it on the other side of the glass.

One day, when he was stronger, his fingers would touch that fascinating skin for real…

One day, when he would wrap them around the merman's throat and squeeze the life out of him for daring to threaten Tom.

Harry weightlessly floated from one moon to the next, diligently doing his chores during the week so Remus would let him join the night hunts every once in a while. The old hunter seemed quite impressed with Harry's hauls, though had expressed concern over exhaustion. It was true that fatigue caused him occasional problems after a double hunt with household duties in between, but Harry napped when he could and overall found it highly unfair that Remus denied him to join more often. He'd considered asking to be switched to the night roster entirely, though that would come with the limitation of not having enough time to gather several hours' worth of food in the mornings, food he needed to present at night to cover for hanging around the castle for hours at a time.

He'd gotten good at travelling back and forth so quickly that he could visit between head counts now, extending his visits into the deep night until his human had to leave or nodded off against the transparent barrier separating them. As it turned out, people did generally sleep a long, uninterrupted time at night, he'd just been lucky to have met one of them who needed less than the others.

The temperature of the lake had dropped significantly. Soon, the Elders would gather for their yearly trip to the surface. How Harry wished he were old enough to count amongst them… How he longed to crawl onto land and grasp tightly onto the one he'd fallen so deeply for. How would it feel to hold a hand that had barely any flesh connecting the fingers? They looked like sticks, similar to the pieces of driftwood that sank to the bottom of the lake after becoming water-logged.

Harry's own hand itched to feel it, to learn of its texture. Would it be as smooth as the pudgy, pink clams the flesh resembled? Or alike rough wood?

It'd been a bit of an adjustment to see humans into a new light after the initial confession, but Harry proudly thought he'd gotten better at noticing details in expression rather than focusing on the strange tint of the skin. Each night, the longing to know more, see more, grew exponentially.

''I wish you could tell me your name,'' Harry expressed one night.

He was granted no more than a sad smile at the question. About a moon ago, the other had tried something, drawn fiery shapes into the air that looked like letters, though unfortunately of a script unrecognisable to Harry. The only thing he'd learned from it was that the name consisted of three characters, which wasn't much to go on as he knew nothing of human names or how it would translate into mermish. He'd suggested to be taught to read the script, by Harry saying a word and having it written out by the other. It'd been refused with a sharp shake of the head, which he didn't know what to make of. It had hurt for a moment until realising that perhaps it was not that easy to translate their languages.

So, Harry surrendered for now, contenting himself with the company, separated by the wall of clear quartz.

''Perhaps in your second year,'' Slughorn indulgently smiled at Tom's request to be given a permission slip to the restricted section. Hogwarts had become his home in the past months, each time of the year giving off a distinctly different feeling while a constant reminder remained of that he belonged. It was thus infuriating that even a single room in the castle was so off-limits. By now, he was able to waltz into the staff room or teacher's quarters for a chat (except for Dumbledore's, but he avoided the mean-spirited professor like the plague, so it wasn't a loss worth counting), so why wasn't he trusted with this?

He stood straighter, trying to imitate the vocabulary he'd quickly picked up from Pure-bloods who'd been trained to act like royalty all their lives. With pleading eyes that he'd copied from Edmund Rosier and a hopeful smile he'd learned earned favours from observing Walburga Black, he looked up at the Professor. ''Sir, I urgently need to research a topic that older students told me only the restricted section may have books on…''

''Requesting a specific book would be no issue, Tom,'' his head of House sighed as if willing to compromise. ''If there is a title you need, say it and I'll see what I can do. However, I cannot in good conscience let a first-year student walk among the shelves of the restricted section of the library, pulling books off the shelves in hopes to find something you won't even inform me of!''

Sucking in his breath through his teeth, Tom weighted the options. Initiating a teacher in his plans (a teacher who had quickly started to appreciate Tom's talents) would give him access to avenues he couldn't take before. On the other hand, Slughorn was rather skittish about practical magic and if Walburga was correct in her explanation, the only way to break this curse would be by casting another one – forbidden at Hogwarts for even much older students. Dark magic was practised in Slytherin under blind eyes, sure, but Slughorn would never condone openly planning a dark ritual.

''I can wait till my second year, Sir,'' he replied with a forced smile. ''Perhaps my panic was… unwarranted. I'm so sorry to have bothered you. If I find the title of a specific book that could aid me, I'll approach you again, if that is alright?''

Relief flooded Slughorn's rosy face. ''That's perfectly fine, Tom. Keep up your studies, I will consider it next year if your exam results are stellar and you agree to be accompanied by a Prefect.''

Now that would be interesting, considering the dilemma of no older students wishing to offer aid. If a teacher ordered them, could they refuse? Or would they pretend to go and abandon Tom in the library? Just in case, it might be good to acquaintance himself with the current Prefects.

Never one to wait for the iron to cool, Tom lingered around the entrance to the Slytherin common room until he spotted the first one: a stern sixth-year with strikingly blond hair. A discreet cutting charm and a bit of a scene later, during which Tom helpfully jumped in to organise the Prefect's essays that had gone flying every which way in the dark corridor, he mechanically accepted the hand the older boy held out.

''No word of this embarrassing accident or I'll skin you alive,'' the Prefect said with flushed cheeks. ''Hey, you're that first-year all the teachers are mad about, aren't you? Riddle?''

''Yes, Sir. Though I wouldn't say all teachers. Dumbledore is difficult to please.''

''Don't take it personal, he holds great disdain for all Slytherins. Ah, where are my manners. Abraxas Malfoy,'' the boy offered with a tight smile that did not reach icy eyes. ''I'll return the favour one day as long as you keep your mouth shut, understand?''

How absolutely perfect. Tom might start to like his luck one day.

Goals clear and set, Tom poured all attention into his official studies, Easter break passing by in a whirl of essays and potion practise with the only interruptions being Harry's regular visits on every seventh day. Having learned about the significance of the number by now, Tom knew this was no coincidence. The visits were like clockwork, which served to heighten his paranoia. There was deep magic at work that pulled Harry towards him, to remind Tom of his cursed fate.

As the plans for further research into curse breaking had been forcibly put on hold and all accessible books on merfolk had already been memorised, the only extracurricular activity Tom focused on during those quiet nights was researching ways to shield and arm himself against the specific dangers that the lake brought. After all, merfolk hunted underwater, so it would make sense if Harry would try drowning him first. So far, he'd found multiple ways of breathing underwater, though only the bubble-head charm was somewhat feasible. It was a sixth-year-spell that required only his wand, whereas other methods relied on ingredients too expensive to order and not available to steal, or on human transfiguration that only the advanced transfiguration class mid-seventh year received instruction on. The Bubblehead charm was difficult to practise, though, with only a shower available in the dorms.

He'd heard the prefect dorms had baths, so he added 'become a Prefect' to his list of personal goals out of principle, even if Tom was certain he'd manage to find a way to master the charm far before fifth year rolled around.

Somehow, his every current action had come to revolve around the looming threat, from advancing his normal studies to impress Slughorn enough to allow access into the restricted section, to practising magic far above what his teachers believed suitable for a first-year student, to adopting Pure-blood manners as easy practise for upcoming interactions with a wholly different species.

Perhaps next year, he'd start looking for a tutor in mermish, just to be on the safe side. Harry might be less inclined to instantly attack if he could hear Tom pleading before being dragged under. Long enough to gain the upper hand and strike first.

It was a shame that Harry's surprisingly insightful suggestion about learning the alphabet couldn't work. With mermish being an inherently magical language translated to any listener to one's native language when spoken underwater, the letters would hardly correspond to what Harry was actually saying. It was a miracle that it wasn't translated back to screeching when pushing through the window – perhaps because more magic was in play for the transfer.

Sometimes, on evenings that Harry had more to sing than to say, Tom suspected that the music messed with his head, for the melodies – simple as they were - had a calming, almost drowsy nature to them. Each time after the singing died down, he avowed to walk away next time.

He never did.

Cheerful laughter, tearful goodbyes, parties and games made the common room buzz like it was Christmas again. No, more than Christmas, for now no students were absent. Tom took in the scene with a scowl, nursing his bruised pride after having been denied staying over the summer holidays. He'd asked Slughorn, who'd promised that he would try… then promptly took it up with the wrong person. ''I cannot possibly go over someone's head and take it up with Headmaster Dippet before having had the ear of the Deputy,'' Slughorn had defended himself when for the first time since attending Hogwarts, Tom had openly shown anger towards his Head of House.

Dumbledore had said no. Of course Dumbledore had said no, he hated Tom. It was so obvious, ever since that first visit, that the Transfiguration Professor cast judgement on his every action for reasons unknown.

''Bugger off,'' he snapped at Walburga before she could slide into the seat next to him.

The girl paused, scowled and abruptly turned, staying only long enough to tell him: ''Fix your attitude problem, Riddle. I was going to invite you to stay over the summer at my place, but I've no need for unpleasant company.''

Nails bit into the palms of Tom's hand as she strode off, something acid sliding through his body like a venomous viper. Throwing something like this in his face while making clear she'd taken the option off the table meant nothing but cruelty. Besides, he had no assurance of whether the offer would actually have been made if he'd been nice to her. He could not rely on Walburga or any of his peers. Not unless they were so far beneath his boot that they wouldn't dare invoke his ire.

Still scowling, he fantasised about his future reign of the school while waiting for the pesky people to clear out the room. Today was a Sunday. The last Sunday of the year that Harry could visit him.

''Miss you miss you miss you,'' reverberated through the near-empty room. Beyond the glass, Harry's face was scrunched up into a grimace of utter, devastating sadness.

How had the merman even learned of Tom's imminent departure? Was he that observant, seeing the packed trunks and cleared common room? Or did his kind keep track of when they'd have the place to themselves?

The words struck a chord within Tom's chest that he hadn't thought existed. He'd never been missed before. It felt as if his frayed heart was being mended, Harry holding a needle and thread to carefully sew together the pieces everyone else in Tom's life had torn from it.

Seeing the absolute distress over his leaving brought a flash of clarity. Harry may be fated to kill him, but it wouldn't be done with malice.

He had seen the creature as an enemy all year. A wild animal out to strike him in a moment of weakness, toying with its food. That had been an error - or better said a misunderstanding as Tom did not make mistakes. Now, he understood how they were both trapped in this curse, and from all their get-togethers over the year, from everything Harry had sang through the glass, Tom concluded the other boy was not even aware of it.

Oh…

Now he needed to break this curse for the both of them.