AN: I started this fic 2 years ago, after finally watching the last part of the Durarara anime, and could no longer resist throwing my hat into the hanahaki ring.

The bright lights of the city at night left ample shadows for certain individuals to conceal themselves in. For today, Orihara Izaya preferred to hide in plain sight. He sat on a park bench, underneath a fading streetlight, watching the world – his beloved humans – pass him by.

A light breeze brushed at his hair and theirs – the couple walking along the path in front of him. A man and a woman – her clinging to his arm like she was claiming it as his own; him, smiling down at her like she was the only human in this world worth loving. Did he want that? It was awfully impractical. Stupid even. If anybody should jump out of those bushes over there, they were dead.

Across the street, a black cat drew alongside a woman waiting on the pavement. Her face was caked in make-up, an impenetrable mask of availability. A man leaned out of the window, beckoned her in. As she clambered into the car, her skirt rode up, clinging to the tops of her thighs. The man inside licked his lips.

Did Izaya want that? Certainly not. Watching his humans go about their daily lives was one thing. He lived for that, existed to disrupt it. But him personally? Engaging in things like that? Spending time with people? The same person, over and over? Holding hands with someone as he walked down the street? Definitely not.

So why then was this happening to him?

"You know, you should really arrange for your daddy to have someone pick you up this late at night."

The voice was familiar. Tom. He was crossing the park behind Izaya. There were more footsteps. Three people.

"W-well I thought Kururi and Mairu were going to be there so we could walk home together but..." The Awakusu granddaughter.

Izaya flipped the hood of the parka he was wearing over his head, heart pounding in his chest. A bottle of pills rattled in his pocket and he froze. His breath caught in his throat, a familiar tickle beginning to burn.

Keep it in. Keep it in. He couldn't fight Shizuo here. He couldn't draw attention to himself now.

He was thankful that he'd had the foresight to wear something other than his usual wardrobe. The parka Namie had left in his apartment was big, bulky and a pale green which screamed 'Not Izaya' and had a hood so large that it shaded much of his face.

"It's alright, it's alright," said Tom, coming into view. He was walking in front, turning back with hands raised like he was soothing a frightened animal. "We have to pass by anyway, don't we?"

Behind came the little girl, clinging tightly to Shizuo's hand. Her cheeks were flushed with embarrassment, her eyes downcast.

"Yeah, don't worry about it." Shizuo turned his head towards the little girl, expression soft, warm. Izaya thought he saw the monster give the girl's hand a little squeeze, but she didn't squeal or flinch so he couldn't have done.

She smiled.

The next thing Izaya knew, something was choking him, crawling up from the back of his throat. It was all he could do to double over, hand clamped to his mouth, and try not to vomit until the coughing was over.

By the time he could breathe again, Shizuo, Tom and Akane had crossed the road and were disappearing down a side street, out of view. Only Izaya remained, leaning heavily on the arm of the bench.

Underneath the streetlamp a half-unfurled flower stuck to his palm.

For a moment, he simply stared at the ironic suggestion of white petals, echoes of his earlier conversation with Shinra dancing in circles in his head. Then the laughter forced its way out of his throat just like the flower had.

Three days earlier:

"You probably have a chest infection," Namie told him curtly, placing a cup of tea within his reach violently enough that it made an irritating clattering sound but just carefully enough that it didn't spill, limiting his ability to complain about it.

Before a retort could form on his tongue, he was coughing again into his elbow. The ever present tickle in the back of his throat felt like it had formed a lump, like he'd swallowed a spider and it was somehow still living in his oesophagus and now it wanted to crawl back up.

Sickness was annoying. It was just one of those things. Steps could be taken; measures could be put into place and as a rule, Izaya Orihara rarely picked up the illnesses of the human beings he preferred to observe from afar. But it did happen. And when it did, it only served to remind him of his underlying humanity – the worst parts of it.

There was a chill in his bones, a lethargy that was only eclipsed by irritation, and his body would not stop trying to cough something up that so had so far proven to be nothing more than the occasional glob of hideous yellow mucus. And it had been this way, slowly worsening, for a month now.

Namie didn't give him the chance to stop coughing before she spoke again. "Of course, it could always be something worse, you know. The longer you leave it, the worse it will get. Don't you have-"

Panic flashed in his eyes, rose like bile from his stomach. He lurched forwards, hanging over the arm of the chair and coughed so hard that it felt like he was retching. He barely heard the sound of something solid hitting the ground over the sound of his hacking coughs but he felt his throat constrict, felt it fall from his tongue.

Then it was over and he was staring at Namie's frozen feet as struggled to draw breath. A strangled gasp left Namie's lips and for a moment, Izaya almost expected her to start coughing too.

"You need to call that underground doctor," she finally said, her voice strained.

He wiped the moisture from his eyes and the trail of saliva from his chin. On the floor, directly beneath the place where he had hung his head, sat three green lumps. With a sharp breath, which irritated his throat, Izaya reached down in simultaneous fascination and disgust.

The object was sticky with spit but he brought it to his face, turning it over in his fingers.

"It looks like…"

"Flowers," said Namie, taking several steps backwards. There was finality in her tone and something worse.

"… a bud," Izaya corrected, pulling its opening like there were answers inside.

His mind had simultaneously ceased to function and gone into overdrive, offering him nothing to work with except that this didn't seem very human. That he had no clue how this had ended up inside him. That he had no idea how he hadn't known of it.

"Do you want to call or shall I do it?" said Namie.

When Izaya looked up there was something similar to fear in her eyes. But what had she to fear? That this was the beginning of some new and deadly disease? That he was undergoing some hideous metamorphosis before her very eyes? No, that would amuse her. No, she knew something…

"Namie," he said, voice low and husky from the coughing fit. "Explain."

She dodged his gaze. She was frowning, face pale under his artificial lighting. "I think it's best the doctor explains – but I am not cleaning that up. You'll have to do it."

"What have you done?" he growled.

At this, she turned to look at him, a new emotion at the corners of her lips. Disgust.

"Nothing," she hissed. "This is all your own doing. Now if you don't want me to call that doctor, my shift is long over and I'll be taking my leave."

With that, she crossed the room, barely pausing to pick up her handbag on her way to the door.

"Namie," he warned. It was both a command and a promise.

"Call the doctor," she repeated. "I'm a scientist, not a medical professional."

He fixed her with a look but the tickle returned. His eyes began to prickle with the strain of holding it back. The cough tore its way out of him before he could force her to explain.

The door creaked as it opened. Before it closed, one word was shot back into the apartment, quietly, like Namie hadn't quite decided whether to share it.

"Hanahaki."

It took two days before he was able to see Shinra. The underground doctor had been on yet another trip with Celty and had cheerfully told him that even if Izaya was dying, he could hold on until the trip was over or go to the hospital and since he wasn't dying, he could wait. Probably.

Namie had rather unconvincingly called in sick too, leaving Izaya to work alone armed with a single word shot his way by a secretary he should certainly fire and the internet. His actual job had been slow with only two requests for information reaching him and those for things that he already knew all there was to know about.

This had left him ample time to trawl the internet.

It wasn't especially productive. Googling his symptoms generally let to the advice that he should see a doctor. There were a lot of conditions indicated by coughing up mucus, or blood, or even half-digested food. Since Izaya didn't recall eating any flowers, he decided that none of those quite fitted his experience.

Hanahaki, which was listed on some less reputable looking sites, seemed to largely revolve around urban legends and literature and didn't seem to have much to do with Izaya either. He wasn't coughing flowers. He was coughing things that looked like buds. He had never experienced love of any kind, barring his love for all of humanity of course. Besides which, he didn't know of any medical condition that revolved around the physical manifestation of symptoms which were caused by such specific, intangible emotions linked to affection for one particular individual.

He would sooner have believed that Celty's memories actually were stored up her anus than an illness such as this one – especially suffered by him.

By the time he arrived, breathless and a little light headed, at Shinra's apartment, he was no closer to an explanation and itching to destroy. If he had been feeling better, he might have deliberately located Shizuo and thrown something at him out of the sheer injustice of the situation and the fact that, as a monster, it was acceptable to blame Shizuo for unpleasant situations.

But he wasn't. So instead he huddled in the large parka Namie had abandoned in her hasty exit, which he had put on partly to disguise his identity and partly to cough all over out of spite, and quietly allowed himself to be ushered in.

All in all, he felt so rotten that he explained his plight with minimal sarcasm and sat hunched and miserable but unprotesting on the bed in Shinra's guest bedroom while his childhood friend pushed a cold stethoscope onto what felt like every patch of skin his ribcage could offer. He tried to contain his urge to cough as he was told to breathe deeply, sat still and unresisting as blood was taken from his arm and swallowed his pride to pee into a container, which Shinra put on the side and did nothing else with.

Finally, he coughed out two more buds and allowed them to fall into the bedsheets in protest of his harsh treatment.

Shinra had the nerve to look pleased by this. He showed none of the reluctance Namie had, immediately pouncing on one of the buds and examining it closely. He said nothing else until he was done examining it, then he picked up the other one and threw them both in the bin.

"Well, it's definitely Hanahaki," he diagnosed finally.

Izaya fixed him with a glare.

"Yours is the first case I've personally seen." He sounded entirely too happy about this. "I don't know how much you know about Hanahaki."

"It's a romantic construct to portray unrequited love in poetry," Izaya responded dryly, citing one of the definitions the internet had given him.

Shinra raised an eyebrow. His smile, if possible, grew wider. "Well, my beloved Celty is widely regarded as fairytale but she's only my happily ever after."

He hugged himself and twirled over to the medicine cabinet. Izaya simultaneously wanted to make a scathing comment but couldn't find the words or energy to argue with that.

Digging through the bottom drawer, Shinra continued, "But you're not entirely wrong. Hanahaki is defined as a disease in which plant-like parasites grow in the host body, in response to specific emotions, those emotions being unrequited love. There are multiple strains of the disease. Pulmonary Hanahaki is one of the rarest but Nebula has been studying it for quite some time so - I'm sure these are in this cupboard – I'm confident there are different treatments you can try. Ah! There it is."

Shinra was by now half inside the cupboard, different pill bottles forming a makeshift fort around him.

Izaya coughed weakly into his hand, mind racing.

"You haven't recently lost a mysterious lover, have you?" said Shinra, pausing in his search.

Izaya choked. Shinra quickly grabbed what looked like a bedpan and threw it in his direction but Izaya swallowed the spit he had been choking on and the bedpan remained empty.

"What do you think?" he spat.

Shinra looked at him, a smile in his eyes, and waited.

After a long pause, Izaya answered anyway, irritation dripping from the word: "No."

"Thought not," said Shinra brightly, returning to the cupboard. "Hanahaki is quite common in people who have lose a loved one – mostly the elderly but younger people too. It gets into the bloodstream, takes root in the heart and then bam! Heart attack. Of course, the flowers disintegrate quickly after death… Victims don't even know they had it. I assume they think they're just dying of a broken heart. Or maybe they don't think anything at all."

A pill bottle rattled in the cupboard and then Shinra was dusting it off and holding under the light by the window. "That's the one!"

He grabbed a pen from the side, next to the forgotten urine sample, and scrawled something on the label.

"Like I said, there are multiple strains of Hanahaki and even in similar strains, the disease progresses at a different rate in different people. Your flowers aren't fully formed – that's a good sign. But if you're coughing plant matter, then it does unfortunately mean that the roots are spread out through your lungs. We will X-ray you to assess the extent of the damage."

"What then?" said Izaya.

The urge to cough was building again in the back of his throat. His chest felt heavy, the diagnosis undecipherable.

Shinra smiled, his shoulders lifting slightly. "You take these pills and hope it shrinks it enough to surgically remove the matter. Of course, spores might linger, so you'd need to keep taking the pills afterwards but that's all dependant on the success of the treatment in any case."

"And if it doesn't shrink?"

Shinra's tone didn't alter. He continued to smile, but his words sent something sharp and cold deep into the pit of Izaya's stomach.

"Then you take those pills and hope it slows the progression of the disease for a while."

Izaya opened his mouth to demand an exact prognosis but Shinra cut him off. "There is only one known cure of Hanahaki this far advanced. Unrequited love is the main condition for the disease to take root. Obviously, if your lover is dead, they can't very well reciprocate, but if the person responsible for those feelings is alive and well then…"

"There isn't anyone…" said Izaya.

Shinra raised his eyebrows, the look in his eyes clearly stating that he thought Izaya was lying or else giving a stupid response.

Izaya returned his look with a tired yet firm stare.

Shinra simply sighed, offering him the bottle of pills to put away. "Take these three times a day with food. And consider it."

"Consider what?" Izaya said sharply, ripping the bottle from Shinra's hand.

"Figure it out," said Shinra, smiling a knowing smile before clapping his hands together. "Right, let's organise that X-ray."

Those words boiled in his blood, itched beneath his skin, burned at the back of his throat and haunted him all the way to park, where Shizuo and Tom were walking the future Awakusu heiress home.

AN: Thank you for reading! All reviews are greatly appreciated 3