A/N; I blame cywscross and his MoD!Harry fics. They teased my muse and I have had OP on my brain for a while now. So that's how this two-shot started.
I didn't mean for it to turn out in such a way. This isn't my usual style either...

Harry Potter lived an ordinary wizarding life after his victory over Voldemort in his youth. He worked in the DMLE as an auror, married a witch, had children, got promoted, sent his children off to Hogwarts in due time and lived an ordinary life. He grew older, watched as his children married, became a grandfather, and other ordinary things that a wizard would do in his life.

Harry Potter would say that he was no hero. Just an ordinary person who became exceptional through the hardships and circumstances he endured in his youth. For that it was a hero was, he would say. An ordinary person deciding to do the right thing over what was easy -and in many ways he was a far greater and nobler person than many for that as he didn't just say the words -he lived them.

So Harry Potter lived the life of an ordinary wizard for all his famed heroics and brave deeds. His life was notable but nothing exceptional. He didn't end prejudice. He didn't break monopolies. He didn't muddle into politics either. He lived an ordinary life and then he died.

His funeral was well-attended. Witches and Wizards stood for hours to be able to lay flowers on his grave monument in Godric's Hollow.

In life, after all his heroics, Harry Potter finally had his wish for normality and ordinariness for a wizard no matter how extraordinary his adventures might have been. In death however, Harry Potter became something else. He truly became the master of death. Something that no one had ever achieved before.

Death contrary to popular belief is not some personification of any one thing. That's just how the limits of our human minds interpret it. Death is not a skeleton in a black robe carrying a scythe. Death is not the slow breathes becoming ever more shallow and stopping as someone strangles another. Death is not a man slowly wringing off the cap to a bottle of medicine and downing more pills than he should so that his demise would be quick and not a slow painful decay over months. Yet we say that this all is death.
People give death fancy names. A personification, idea, homicide, suicide, massacres, epidemics and genocide.

What Death truly is was a force. A force of chaos. A force of decay. A force that ends and in that end provides for the living.

Now newly dead Harry Potter is the master of this force. As he ever was and will be.

Ace first saw the man when he was four. He had first seen the man when he was coming to in the jungle after his shitty jiji had knocked him out and left him there. The man ruffled his hair and touched a tender bump. Ace hissed.

"Nasty bump you have there, kiddo. Tell your shitty jiji to be more cautious. He almost killed you. Pity that."
"Who the hell are you?"
"Just someone passing through. We'll meet again, eventually. I met lots of people that way."

The strange, cheerful man pressed again on his bruised head and it throbbed. Painfully. By the time Ace stopped hissing in pain he had resolved two things. One was that the next time they met, he would do his damnest to give that man a taste of his own medicine. Second was that he wasn't going to cry ever again.

The second time Ace saw the strange man with knowing green eyes was when he was seven. He had beaten a few men up who were speaking about what they'd do to Roger's kid if he had one and insulting the bastard all the while. The only people that could do that were the ones who had met, known and been victims of that bastard directly, Ace thought.

He had been breathing heavily after beating up three grown men. He hadn't hit them too hard, he thought, but they'd certainly know better that to do that ever again. That, the son of Gol D. Roger was certain of.

"Ah. Poor bloke. Underestimated how vicious children can be." The strange man tsked at the guy that Ace had tossed into the wall.
Ace recognized the man and swung his fist at the man's jaw and hit the wall instead forming cracks.
The boy looked around for the man, even scrambling to the nearest balcony and rooftop and had no luck finding him.
The man with knowing green eyes and messy hair had vanished into thin air.

Ace, Luffy and Sabo had sworn brotherhood. There should be no secrets between them. At least in theory. Luffy didn't have any beyond his heritage that he didn't know about and Ace had long since suspected that Sabo was from a higher social class. While his heritage was something that should remain secret, he shared it with his brothers.

He didn't tell them about the man he had only seen twice.

The next time he saw the man, Sabo had been taken back by his noble family, the captain of the Bluejam pirates was trying to kill him and Gray Terminal was on fire.
It was only a brief view of the man, and he was busy fighting the pirate but the man gave a cheery wave at him. He growled and attacked the pirate all the fiercer. After knocking the pirate out and leaving him to his almost certain doom Ace picked up Dadan and ran from the burning stink of garbage all around him.
He turned back and saw the strange man lean over the pirate. The man looked his way. Ace flipped him off.

After Sabo... died, he and Luffy were at the cliff that overlooked the bay.
They had to get stronger.
Ace promised Luffy that he'd never die.

The words had a strange and nasty taste to them.

Ace saw him a number of times more as he was getting used to hunting the more dangerous beasts solo.
The man would say hallo, and Ace told him to fuck off, get lost or stop stalking him.
The man would wave. Ace would curse with his hands.
The man would ruffle his hair. Ace tried to break his jaw, ribs or something and failed as the man danced out of the way.
The man would disappear. Ace scowled and seethed in anger.

The only correlation that Ace could find was that the closer he or another person was to dying the more often the man appeared. As he got stronger, he saw the man less and less.

He was in Goa again and thirteen when he next saw the man.
More than a few people remembered his younger antics and held grudges. They also knew they were weak and had banded together.
He was far stronger than they were, but they far outnumbered him and they had better weapons than their fists. Getting shot at was a new experience for him.
He would get a few bruises and a knife had slashed deep into his left arm. Not enough to cripple but enough to leave a scar. He took the knife as a hard won prize. This, Ace thought, was why nakama for a pirate is so important. Having someone capable to watch your back while they watch yours. If he wanted to make his own name and fortune one day, he'd need nakama or else the Grand Line would kill him.

Ace saw the man appear as if he'd always been there.
This time, Ace decided to be polite.

"Hello. I'm Portgas D. Ace. Nice to meet you."
"How polite. I'm Harry. I meet everyone eventually."
"Everyone?" Ace asked, disbelieving that.
"Yes. They usually don't like to see me, if they actually can. You might want to keep that knife. It's a good one." The man wearing round glasses over green eyes with shaggy dark hair told him.
Recognizing that it was a good knife, Ace decided to keep it and make use of it.
"Can I ask a question?"
"You can, but I may not answer."
"How do you keep popping up and disappearing?
"That's an easy one. I'm everywhere."
The man -Harry- disappeared like he's never been there.

Ace thought on the riddled answers.
His only conclusion was that he sucked at riddles.
He kept falling asleep whenever he tried to answer it.

He never told Luffy about the mysterious man either.

Ace didn't see the man again until he was seventeen, celebrating on the beach with his nakama.
They had found a devil fruit, and Ace was planning to eat it. The Mera Mera no Mi was a powerful fruit.
They had fought for it against another crew and they had no serious injuries but had sent the other crew off packing and limping away. A few sprains, some heavy bruising, and one guy with a slight headache but everyone was alright.
The man flickered in and out of his sight once and so Ace found himself wandering away so they could have a private chat.
"You haven't figured it out yet, have you." The man -Harry- said conversationally.
"No. I haven't."
"You've had a bunch of clues and hints already. It's sort of surprising."
"How is anybody supposed to figure that out? Is it some sort of devil fruit?"
"Nothing like that. I suppose you'll figure it out soon enough."
Ace threw a punch at him but it didn't connect.

Ace returned to the celebration and ate the devil fruit drawing a cheer from the majority of his crew and a lot of laughter for the face he made while eating it. The fruit tasted like his promise to Luffy years ago. He quickly washed it away.

He figured it out in the morning. Vaughn had been nakama and now he was dead. His doctor had informed him and the crew tearfully that he had missed the signs of internal hemorrhaging. How was easy enough. Vaughn had been a bit standoffish, but there when needed. Vaughn also wasn't one for lingering long in celebrations as he'd find something quiet to do as he sat back, watched over them celebrating while he sipped his drink. While Vaughn slipped off, unaware that he was slowly dying, since the only apparent injury he had was already treated, they had celebrated.
Ace told his crew to find some wood for a pyre and told his doc to make damn sure that next time everyone was okay.
He found it strange that the first intentional fire he started with his new abilities was a pyre.

He had also figured out who or what Harry was.
Odd to think that death's name was Harry of all things.
He was also decidedly not a skeleton. He'd ask about that next time.

Next time was that very night. He had relieved the man he had assigned to the night watch and sat on the crow's nest.
"Death comes in many shapes and forms you know."
Ace would deny ever startling at that.
"And people are always giving me too much credit. Everything dies, decays and gets reused eventually. Sometimes people help it along. That's generally called killing, or murder. Sometimes it's planned genocide or an accident. While everyone will eventually die, how they die is up in the air. Vaughn could have mentioned not feeling right, had the doctor look him over and still be here. He didn't so he's not."
"You could have told me that. He's my nakama and I'm his Captain." Ace said flatly.
"And I'm the Master of Death."
"Master of Death? What the hell does that even mean?"
"Not a lot actually. It's pretty self-explanatory. The job and everything."
"So you're a god then?"
"I don't think I am. I distinctly remember dying as an old man. Had a wife, children, great-grandchildren, well-respected. The works. A solid pillar of the community. What's odd is that you can see and interact with me. Most people avoid me and all that I am."

Knowledgeable green eyes gazed into his dark ones.

"Ah. That explains it."
"Explains what?"
"Nothing and everything."
Ace throws a fist and fire travels along the path of his swing.

"Nice shot." He heard next to him. "You've just killed fifteen people and severely burned another eleven. Three are dying of smoke inhalation. Oh, and you just wasted a good stock of tea too. Sinking the ship, boiling the water and the fish enjoy the tea. Someone needs to teach you to properly appreciate tea."
Ace blinks in confusion as a few of his subordinates come on deck to see what he'd done.
He jumped down from the crow's nest to deal with that as it was something he knew how to deal with.
Dead men scolding a living man over wasting tea was weird. Even for the Grand Line.

Harry visited him from time to time as he blazed a trail through the first half of the Grand Line.
Sometimes he made odd comments, observations and sometimes Ace thought the man was crack'd. Like now. The man was lamenting the fact that there were no dragons around. At least naturally occurring dragons, the man amended. He had a friend that loved them and had hatched one in his house and another dragon he had rode as he had broke it out of its prison.

It made Ace wonder exactly when the man had died and how had he been a pillar of the community with some of the things he had allegedly done.

At Sabaody Harry had gotten a little weird. Not that anyone else could tell as no one else could see him. In an effort to not appear as crazy as Harry was, Ace didn't react to Harry all that much.
So the man had turned to commentary. It was informative even if Ace's was uncertain of how accurate it was.
Harry flickered out for a moment and reappeared. "Sorry for that. Suicide. It was the only path of quick revenge available. Blood got everywhere. That suit is ruined. Stains are never going to get out."
Ace blinked.
"She bit her tongue off and while dying she killed a number of people. Then she went boom from the collar. Brave girl that."
Ace bowed his head in acknowledgement.
Harry had seen all sorts of deaths over the years. He chatted about the notable ones and the most recent ones. He never brought up Roger's execution which Ace was thankful for.

Ace didn't see Harry again until after he had met up with Shanks so he could thank him for saving his little brother's life all those years ago. Ace's smile at the amiable parting was large as Harry was fluttering around the crew, looking very silly as he posed in awkward poses and spazzed around a few pirates.
He might not have known a lot about Harry but Harry was only that chipper when someone was most likely going to die an amusing death. Very, very soon.

During the space of time when he was trying to kill Whitebeard, Harry was practically a constant companion.
It didn't make him any more amendable to joining and having a father. He was happy not having one.
It also helped that Harry's suggestions were good ones. They still met with failure, but that was clearly on his part alone.
He really should have let himself rest and heal up. He would have met more success that way. Harry told him that he still would have failed but at least he'd leave a mark.

Harry disappeared for the longest time since his childhood after he had accepted Whitebeard's offer to become his son.
He showed up again during the fight against Doma, frowned and left without a word.
He then later showed up and repeated the same, the day after his promotion to commander.
He showed up again, woke him up and dragged him towards the deck where he found out that his fellow commander Thatch had been killed. He stormed back to his room where Harry handed him his bag that he had packed and stormed back out ignoring his brother's calls. Harry hitched a ride on top of his sail.
He still wasn't sure if Harry actually was a god, or a deluded ghost who's ability to determine who's dying and how was godly or not.

A number of leads proved to be a bust.
Harry flickered in and out for hours or days at a time now that Ace was alone and could truly interact with him for more than stolen seconds at a time.
Ace had thought that since Harry knew when someone died that as soon as someone was killed around Teach that it would be easy to find him.
Instead it got him a lecture on metaphysical forces, mental constructs and how keeping track of everything that died was fucking impossible because in the end there wasn't that much of a difference between a fish dying and a man dying except who ate who. Except for the ego.
Apparently most souls didn't know shit as soon as they left their body and to find someone that way would mean that he had to know the person's name and call them with their name, appearance and personality up which really wasn't worth the hassle.

He asked for him to call up Rouge.
Harry said no.
Ace tried to kick him this time.
He failed.

Ace saw Harry flicker in and snicker from behind Smoker.
A warning that Luffy was going to knock them both through walls would have been nice.
How the hell did that even work anyway? They were both logia and he knew how to turn into his element on contact!

It appeared that he was forgiven soon after he burned the ships that Crocodile's agents were on. Soon after he was out to open sea he asked why Harry wouldn't allow him to talk to his mother.
He was treated to another lecture on how souls were managed or more accurately managed themselves.
And people wondered why he wasn't religious in the least.

Ace asked, "Does this make me your prophet?"

"I'm not a god Ace, therefore I don't need one."

Fighting Teach and killing Teach was what he had planned. Being captured by Teach and turned over to the marines to rot in Impel Down wasn't.
He both dreaded and waited with hope as time passed closer and closer to his day of execution.
Harry at least kept a nice stream of chatter up. Not that it was nice chatter as he listed a litany of crimes that various criminals who had died in Impel Down had committed. Finding out that the guards had similar crimes if lesser in scale was not comforting in the least.
He also confirmed the validity of Hancock's statement that Luffy had broken into Impel Down.
Stupid little brother didn't have to do that.

Harry was practically gleeful on the executioner's stand. There was no doubt in Ace's mind that a lot of people were going to die today. And all because of him.
Ace felt that he wasn't worth it. He knew that he was likely to die, but he also remembered what he had promised Luffy.

The improbability of getting free from those cuffs had him happy beyond belief.
Unfortunately, there's nothing worse false hope as Akainu's fist came ever closer.
Harry's cackle rang in his ears.

Ace's next thought was, 'I'm alive?'

Then his mind processed what he saw. Ace had the sinking feeling that this was unlikely to be pleasant.