Timeline:
Begins: During Fifth Year.
Ending: Unknown.

Alterations to Canon:
Retcon of Hermione's nebulous ancestry.

Pairings:
Harry/Hermione
Potentially Harry/Hermione/Tonks or Harry/Hermione/Multi.

Story:
Rather abruptly puberty arrives for Harry with full force. Growth spurts, fluctuating magical strength and heapings of horny hormones. One particularly atypical symptom is that Harry is repeatedly beset by prolonged erections. Becoming aroused he remains engorged for as long as an hour or two, sometimes more. The duration of them is slowly increasing, they can get quite painful and 'self-administered treatment' is becoming distinctly less effective.

It doesn't help that Hermione has recently been visited by a very favourable growth spurt as well, her blossoming curves being one of the primary instigators of Harry's ongoing agony.

After abruptly making an excuse and ducking out on a study period with Hermione in the library Hermione follows, part worried for him and part suspicious that he's hiding something. Witnessing Harry go into a broom closet fills her with an unexpected rush of jealousy which she tries unsuccessfully to dismiss, she finds herself waiting in an alcove to see who this witch is that Harry ditched her to go off and fool around with.

After waiting 15 minutes when nobody comes (and I mean that well and truly) she can't help her curiosity and breaks the locking spell on the door and sticks her head inside... where she finds Harry awkwardly tugging away and whimpering in frustration. Quite a lot more endowed than she expected (and she had to admit to herself she had thought about it) she's caught when Harry hears a noise from the now open doorway and spots her.

Harry hastily attempts to cover up by holding his bunched up robe over his groin, utterly mortified at being caught by his best friend... while fantasising about her. And he's no less petrified when Hermione comes into the closet and spells the door locked behind her. Eventually she gets Harry to tell her what's going on, Harry explains his repeated bouts of 'unpreturbable erections' and Hermione asks if he knows what is causing it. Cheeks tomato red Harry says that this time it was a witch leaning over his shoulder to read a book and her breasts pressing against his shoulder.

Hermione feels a little thrill that she's the one responsible though she doesn't say it. She asks whether he's gone to Madam Pomfrey for help but Harry says he's just too embarrassed. Hermione dithers, she can't just leave him here to 'finish up' and before she can think she says 'Is there anything I can do to help?'. Both of them blush so hard they nearly pass out. 'Hermione?'. Somehow she represses the urge to run and actually considers the naughty possibility of giving Harry exactly that kind of help.

She says she wants to help, that friends help each other, right? He shouldn't feel bad, she's offering and... well he did say it was her fault. Besides it could be... educational. She's only ever seen pictures, there are some things you can't learn from books, after all. Harry considers it legitimately for a moment. His biggest fear that some girl would go and blab to the Hogwarts gossip mill that she'd seen/touched/had The Boy Who Lived wasn't going to happen with Hermione... and he couldn't help but think that the real McCoy would be far more effective at helping him finish than the forced fantasy he'd been trying to use.

Made to sit on a transfigured stool Hermione is soon kneeling before him and begins undoing some buttons on her shirt giving Harry an excellent view. What follows is the most intense experience of his short life as his shyly smiling friend fondles and strokes him to completion in only five minutes. For Hermione its captivating, she feels drugged but totally lucid, she's never felt so excited before and its giving her a thrill she never imagined. She's so turned on in fact that when Harry completes, so does she.

As they clean themselves up and straighten themselves out afterwards Harry breaks the silence to thank Hermione sincerely and Hermione smiles and says that of course she did, he's her... best friend. The hesitation in her wording and their locked gazes indicate to both of them that they are equally aware that what just happened has changed their relationship significantly. But, not entirely, as they return to the library to finish their work, feet playing with each other under the table.

As days follow Harry finds Hermione becoming increasingly tactile, her smiles more knowing, her eyes more inviting and her gait more hypnotic. His 'problem' returns full force and Hermione is already leading him away to a classroom before he even has the nerve to ask for her help. This time she's even more enthusiastic, eventually stripping to the waist in order to drive Harry over the edge and she gets off on it even more.

The next time she is deliberately working to provoke Harry's arousal and doesn't hesitate to go straight to oral. Harry is half worried that whatever is wrong with him is now affecting Hermione and half paranoid that this is entirely casual for her and she's just using him for practice, his low self-esteem telling him there's no way she wants the likes of him. The fourth time it happens they lose almost all control and Harry barely stops short of obeying Hermione when wild-eyed with lust she begs him to take her.

A literal cold shower later with Hermione sobbing that he doesn't want her Harry flat-out tells her that she's the only thing he wants but not just for sex, they kiss and barely stop themselves from starting where they left off. Harry and Hermione go to the hospital wing to see Madam Pomfrey.

Diagnosis:
Harry is presenting with a rare diagnosis, 'metamorphmagus priapism'. The onset of his ability got tangled with his hormones to produce unrelenting erections as his body unconsciously locked it into place with his morphing talent.

Hermione's diagnosis is decidedly even less expected... she's displaying heritage traits of a Veela. Somewhere in her recent ancestry there was a Veela and with Hermione's sexual maturity upon her those traits are emerging, like a heightened sexual appetite (in fact a real hunger that needs to be sated for Veela) as well as intoxication caused by the sexual release of her mate.

Hermione's paternal grandmother was a squib Veela (no transformation, allure or magic but nevertheless the beauty) from North France who fled to Britain during WWII, but he was orphaned when his father died in battle and his mother during the Blitz. Males cannot be Veela, only daughters inherit but the traits can re-emerge in the female offspring of Veelas' sons.

Long Delayed Plot:
Harry sure as hell is unwilling to let Snape see his memories of Hermione so he seeks (competent) Occlumency instruction elsewhere. Avoiding Umbridges machinations is now more important than ever, her reaction to their status as 'inhuman half-breeds' would be very bad - and possibly exploited to trump up charges against them.

At the Battle at the Ministry sees Harry become 'unchained' when Dolohov curses Hermione with the Flaming Cutter, infuriated at the danger to her, cutters and blasting curses take the place of stunners and petrification jinxes. By contrast however Hermione is largely unharmed, due to her Veela affinity for fire. Her repertoire of fire-based spells has grown significantly and more than one Death Eater suffers or dies discovering that most extinguishment spells and even conjured water do not quench her flames.

The Dark Lord attempts to possess Harry and taunts Dumbledore to kill them. Hermione arrives and runs to him against the Headmaster's orders, she tackles Harry to the ground and for the first time unleashes her allure as her hands become wreathed in characteristic Veela (Passionfyre in fanon) flames, snarling that 'He is mine!'. Her presence, power and the claim itself, accepted by Harry, drives the Dark Lord from Harry's body screaming in agony.

Further Fun and Games:
During the following summer Harry and Hermione receive instruction in their new heritages from Tonks and Fleur respectively. Hermione casually enquires if Harry can morph Fleur, the brunette Gryffindor having become decidedly randy around the former Beauxbaton's champion whenever they are training her allure by Fleur focusing hers on Hermione. Tonks discovers them in flagrante delicto and after realising that, no, Fleur isn't cheating on Bill, she agrees to keep quiet. However in time Hermione coaxes out of Harry that he has fantasies about Tonks and asks Tonks for hair, thinking she'll repay Harry's fulfilment of her fantasy by fulfilling one of his with Polyjuice. Tonks, amused, informs Hermione that metamorphmagus hair won't work with Polyjuice... but how would she feel about an actual metamorphmagus herself?