The day after the final battle Harry retrieved the stone, it simply wasn't safe to leave it lying on the forest floor. That night he held all three Hallows and pondered what to do with them. He slipped the cracked ring over the wand and began to roll it up within the cloak. He felt odd, like the world was pausing as he did so. Shaking the eerie feeling he continued. When the cloak was halfway folded he could feel it; a strange vibration emanating from the Hallows. Magical energy began pouring from the rolled up cloak containing the wand and ring. Wondering if perhaps the Hallows were never meant to all touch Harry reconsidered. Before he could decide the cloak began to glow a brilliant red, within its folds he could see the want glow black and the ring a brilliant blue. A moment later the glow expanded and Harry was surrounded by glowing magical energy of all three colors. They wrapped around him painting his skin in vivid colors, he was immobilized as the objects in his hands began to disappear into the glow sinking into his skin. He barely had time to wonder what was happening before his world went black.
The smell of burnt flesh and blood awoke Harry to a world filled with the murmurs of pain. He felt strange, tingling with energy but also filled with a sense of foreboding as he slowly opened his eyes. A few minutes passed and then he beheld the once while walls of the Hogwarts infirmary. They were stain now with occasional blood stains and dust from the explosions that had rocked the ancient castle. He supposed they were lucky the infirmary was spared. His mind felt fuzzy, he knew there was something important to remember but it was just outside of his grasp.
He had no more time to recollect as his world became filled with a sea of red heads. "Mate don't do that!" An upset Ron exclaimed. "Mione found you passed out on your bed, Pomphrey says you hadn't eaten and she told you to or you'd be right back here and now look what happened!" his best friend admonished.
Harry sheepishly looked at Ron, Ginny and Molly. "Sorry, it just slipped my mind. I didn't mean to," he assured them.
"Never mind that dear, the important thing is that you are alright now. If you can't take care of yourself we'll just have to see that you do ourselves, isn't that right?" a worried Molly comforted the boy. Ginny just lay down and hugged her once-again boyfriend to reassure herself he was alright. Harry snuggled with his girlfriend and endured the mild chastisement from his honorary mother with good grace.
An overworked Madam Pomphrey soon ushered them out of the crowded infirmary and urged him to rest. Only a few minutes after they left did Harry recollect what had preceded his blackout. The Hallows had obliterated themselves! Remembering how the transformed magical energy seemed to seep into him Harry worried. No one had commented and from what he could see of his arms he was his normal pale color again. Wishing for a mirror Harry was surprised when one popped into being in front of him. Wondering at Hogwarts helpfulness he observed himself. He didn't see anything different, although his eyes seemed to be a bit brighter. Deciding a more thorough look could wait until he was assured some privacy Harry set the mirror down and took his rest.
After a complete 24 hours rest in the infirmary Pomphrey allowed him to leave and Harry gratefully escaped. He could see the Weasleys waiting outside the open hospital doors and wished he could escape them. As he approached his friends he noticed they were still looking past him. Confused he stopped right in front of Molly and she just continued looking past him. Harry had a feeling this did not bode well but was thankful for the reprieve. Carefully navigating his way through the damaged halls he found an out of the way bathroom. He stared at the closed door and wished he had a functioning wand to cast a privacy lock. No sooner had he pondered that then he felt a small pull of energy from him and heard the door click. Either Hogwarts was reading his mind or he had done wandless magic without trying, the young savior wasn't sure which idea bothered him more. Taking advantage of his privacy he removed his robes and undergarments. The full-size mirror reflected his scrawny image back at him and although not colored red, blue or black he was changed. Again he realized his eyes practically glowed and upon his chest looking like a brand stood the symbol for the Deathly Hallows.
"Not good, not good," Harry muttered as he checked elsewhere. Luckily nothing else seemed out of the ordinary. Still what to do about they symbol? Thankfully few knew the significance of the wand, stone and cloak and those who did trusted him. He could say he put them away for safekeeping and they'd let the matter lie. That is they would, unless they saw his new tattoo. "Tatoos are definetly out this year," he muttered to his reflection. Twinkling eyes gleamed back at him in humor. "Oh no, I've turned into Dumbledore!" the teen cried. Muttering a few choice profanities that would never have passed Molly he wondered what to do now.
Harry concentrated on the strongest glamour charm he knew and watched in awe as the mark seemed to disappear back into his skin. "Well that oughta do, now what do I do about not needing a wand!" he pondered. Harry knew he didn't have much time before the Weasleys found out he'd left the hospital room and they'd missed him. The best he could figure was to avoid wanting something too much so his magic wouldn't react. He could buy a fake wand later and pretend to use it. He'd have to be careful but it was do-able. He certainly wasn't going to tell anyone the truth; he'd be locked up faster than you can say "He's gone Dark!"
The Wizarding World was fickle; the young savior was very familiar with that fact. They loved him for now but how long before they started suggesting he killed Riddle to make way for himself? He was a known parselmouth after all. Not to mention all the rumors of Dark Lord Visions and the smearing from his 5th year. He couldn't afford it to be known that the powers of the Hallows rested irretrievably within him. He trusted his friends but they didn't all know occulmency and even that didn't stand up to veritaserum. Better they not know entirely he decided. Hoping this was his last major surprise he left the bathroom to return to the hospital and his friends.
Three years later a now married Harry Potter labored over a potion during the dead of night. The temporary aging potion wasn't hard but he'd never been very good at potions. An overheard remark earlier that day had led him to this endeavor. At the Burrow for a Sunday Brunch he listened as Ginny light heartedly complained to her mother that Harry had hardly aged a day since he graduated.
Carefully stirring his potion he ruefully concluded she was wrong. He hadn't not aged a day since he graduated. No it was far worse than that; he hadn't aged a day since the Hallows merged within him. With hard won patience he decanted the potion and watched it cool. Taking exactly three careful sips he once again stared into a mirror sans clothing. His vision began to blur with tears he refused to shed as his face matured and body changed slightly in the mirror. Where before had stood a teenager now a young adult was in his place. Forcing himself to not think about all that meant he studied his reflection carefully for the five minutes the potion lasted. After all he'd have to know how the glamour should look if he was going to fake a normal lifespan. Moments later the forever young savior collapsed in brutal tears. He would never die.
A two hundred year old Harry Potter decided it was time. Everyone he cared about from his youth was gone now. He'd had a long and good life. With the strength of the Elder Wand his glamours had never broken. Annually he brewed his potion and slowly adjusted his appearance to simulate the appropriate appearance. He'd lived an eternal teenager past the death of his wife, her family and even more pain; his children. He'd now outlived most of his grandchildren as well. He had a hard time connecting with most of those who remained. It was a different world now and he couldn't really relate to the complaints of an elderly wizard. He was only faking after all; he was healthier now than he'd been when he really was nearly eighteen. Nearly two centuries of proper diet and exercise had strengthened his body into that of a teenage athlete at his peak. (Not that anyone ever saw it of course). Even when he slipped out of his glamours for a night of relaxation as a teenager he had to disguise himself.
He was tired; tired of pretending and even more tired of losing those he cared for. He was fond of his remaining descendents but he couldn't face seeing yet another generation grow only to wither and die. He'd long since discovered that death was denied him. His career as an auror was fraught with injuries and damage that would have killed a normal wizard a dozen times over. He just healed, instantly from deathly wounds and more slowly from those less serious. Harry never did quite make sense of that conundrum. People put it down to his legendary luck that he survived time and time again. Eventually he'd had to retire since it was getting a bit suspicious.
He'd had a good life but he couldn't continue living in this ever dying world. The one good thing about living forever his he had time; time to find a way to die or an escape. He set his affairs in order, hiding away a larger portion than anyone knew in the stronghold none but he knew existed. It would be his refuge. He relocated his now vast library there and made arrangements with the goblins. Those crafty creatures didn't care about immortal wizards. As long as he was a good customer they would work for him. And so he prepared for his death. A few months later his clever flesh golemn breathed its raspy last breath and the world mourned the passing of a hero.
He watched his funeral and snorted at the disgrace it had turned into. His will's instructions for closed ceremony of family only had been run roughshod over and it turned into a spectacle. The cloak's powers kept him safe as he watched the fiasco. Hundreds, nay thousands of mourners had descended on Godrics Hollow to mourn him. There were even cart seller's with memorabilia for sale! Sighing Harry left the Wizarding wolrd and returned to his refuge.
Another century passed in slow study. Knowing the perils of excessive isolation Harry regularly ventured into the muggle world for a bit of interaction. He never made any close friends but had acquaintances by the dozens. He took classes and even obtained several degrees in various fields. His magical studies could only keep him so busy after all. It was easier in the wider world of the magicless to stay apart. Even after three centuries the magical world was still small enough that an unknown wizard didn't stay unknown for long. But finally after all that time he had his solution. He had resigned himself to eternal life, what he needed was company that would stay with him.
In his studies he'd found beings who were effectively ageless; they could die of injury or grief but not of old age. It wasn't perfect but he thought it preferable to the bare century and a half afforded most wizards. They had never been native to this world though. Thousands of years ago the beings of grace and light had visited through portals that crossed dimensions on special days of the year. After decades of research Harry had found the ceremonies to open the portals and was ready. He was comfortable with his refuge though and hesitant to leave it behind. The wonders of magic once again came to the rescue. It may be a bit much to shrink a giant castle meant to hold a couple thousand inhabitants to the size of a doll house but he could do it. Expanding trunks with time stasis spells took care of all he could conceivable need for food and potions ingredients for centuries. And after all if he had to he could return.
And so the Standing Stones of Ireland once again hosted a ritual. Carefully laid spells kept away all others as Harry began the ceremony. Hours later the glowing stones sparked with blue lightning. Lightning that joined in the center and slowly formed into a large sphere of roiling blue energy. Figuring if it didn't transport him it at least had a good chance of finishing him off Harry left the Wizarding World for what could be the last time.