Harry's POV
He should have never opened his mouth.
Saying it was a great year so far was just asking for a godly intervention, which came of course in the shape of a rainy Christmas.
Yet, the mighty force up in the sky forgot one thing, he has magic, and he was not afraid to use it.
Which was why, two hours after he woke up for his daily workout and opening his presents (he got a diamond watch from Luna, who a couple of weeks ago learnt that it was made from pressured coal and made it herself, candies from the twins, and a firebolt broom with no note, which felt like it means Sirius couldn't be original for him), he had to go take a nap to recharge, as he used his entire magical power to fill the castle with snow.
After waking up to the screams of anger of the teachers and joy of the students, he quietly sneaked away to the room of requirements, where he used the vanishing cabinet to go to his apartment, before going to the leaky cauldron and from there, in the floo network, he shouted "Greengrass' manor!" before disappearing.
Daphne's POV
Daphne was excited, not for the fact it was Christmas, no, that was just a muggle holiday she truly didn't care about, she already celebrated the Winter Solstice a few days ago.
No, it wasn't because she got presents, even though it was nice to get that diamond earrings from Lovegood, (though why would she give her such expensive gift?) and the candies she got from Tracy were yummy, even the microbiology book she got from Harry was thoughtful, but no, that wasn't her reason for excitement either.
No, there was only one reason for her excitement, and that was that this day was the day when Harry would finally show the results of his research, and as much as her father told her not to have too much hope, he wasn't the one who had lessons with that guy once every two weeks, who listened to the marvels muggles figured out about the human body, and the ways magic can be used with that knowledge to take healing to another level.
It both amazed her and terrified her, as muggles, who she thought were no better then monkeys, were actually in some ways equal or even better then magical people.
Yes, it might terrifies her, but it also brought her hope.
Hope that her sister would get better, hope that none of her descendants would suffer, hope that this one guy who was her class mate, who was actually younger then her, would be able to do what countless wizards and witches tried to do and failed- cure blood malediction.
With a knock on the door where they have their floo network, Daphne knew he was here.
"Father! Astoria! He is here!"
While her father and sister were rushing down the stairs, she went to open the door while looking at the clock only to see he arrived right on time, 10:15 exactly.
"Hello Harry, good morning."
"Marry Christmas Daphne, hope you're enjoying your vacation at home."
"While we do not celebrate Christmas and the Winter Solstice has already passed, I really hope you also have a nice vacation with your family."
"Oh, no, I stay in Hogwarts for my vacation, you see, no family"
The awkwardness she felt, as she remembered how he was kicked out of his family for no reason but being a Slytherin lasted until her father came, with her sister right behind him.
"Hello Harry, good to see you, how are you?"
"I'm fine, Basitill, thanks for asking, how are you?"
"I'm doing just fine as well."
"Well, I hope after our conversation you would feel even better."
This sentence made Daphne's heart burst with joy, so much so, that she couldn't stop her mouth from going wild.
"Did you do it? You did it, didn't you? You found a cure! What is it? Tell me!"
Usually, She wouldn't be so out of control, and even if she did, her father would admonish her, but this time her father didn't say anything, instead he only had an expecting look on his face.
"Ahhhh, no. I guess I shouldn't have said it like that. What I meant is that I found the exact cause for the illness, and directions of how to proceed to cure her."
Daphne felt like her hopes were shattered, she wanted to yell at him for saying it like that, but she knew it wasn't a smart idea, her father already reprimanded her last time she yelled at Harry that unless we didn't need his help we should never make him angry.
"How about we sit?" Her father said in his diplomatic voice "Would you like some tea?" "No thank you, I just drank some."
That couldn't be true, she noticed he disliked tea, hated pumpkin juice, and she even heard him call, just two weeks ago, butterbear an abomination, the only hot beverage she saw him drink, without considering the occasional hot chocolate, was this foul smelling thing he called coffee. So either he meant he drank some beverage, or he doesn't trust them enough to drink something they made, something to think about.
"Let me start by saying it is a really good progress, we managed to identify the exact cause for the blood malediction, which means we are half way to curing it."
The encouraging words did nothing to her, nor her father, though her sister was a different story.
"Really?! That's good! Isn't it?" Changing her tone mid-sentence as she looked at Daphne and their father's faces
"It is," their father smiled at Astoria and said softly before looking back at Harry "though I would like a deeper explanation about what your research found out."
"Of course." Harry said before starting to explain.
He explained how the DNA of muggles shouldn't change, and when it does, even the slightest bit, it can cause something called cancer in muggle bodies.
He explained how this cancer work and how muggles cure it after a request from father, terrifying all three of them- as having your own body fight against you was bad enough, having to inject poison into it to survive was even worse.
He then explained that wizards seem to have the ability to change their DNA for a period of time without known side effects, as they do in human transfiguration, animagus, polyjuice, and even Metamorphmagus, yet only in one or two of them, you truly change your DNA, as in the others you just super position a different DNA on top of yours, making your body think this is your DNA.
He explained how Astoria's problem is that her DNA is it a constant need to change to an animal form, something that was caused probably by their ancestors, who might have done a ritual similar to the animagus potion before its creation, but passed only half of the results of it to their descendants, letting them change to an animal but not back.
He explained that the physical changes Astoria is having is her body trying to change to an Arctic fox, while the weakness she always has is her magic fighting it.
How the end result is either death, like her family always had, or full change to animal, as some of the other people who had it became.
He explained the five paths they can take on his road to cure her.
1) they can make sure she always have polyjuice potion with her, as long as she never stop taking it she won't change to animal form, it's the quickest method, yet even if she never forgets to take it every hour, making her take it in sleep would be troubling, not to mention that he doesn't know how living in someone else's body would affect her mentally.
2) He can research a way to make the polyjuice last forever, or combine his research with already giving her the potion, yet the same problems are still there.
3) Do the same only with partial transfiguration, with the help of a transfiguration master they can make sure her body still look the same and has no problem, though she would still need constant care from the master and him being willing to sacrifice their magic to keep her in that state.
4) He can research in the direction of Gene splicing- which would basically allow him to insert new genes into her sister as a way to fully cure her, but he did say it would take the most time, and he even said it doesn't have 100% chances of success.
5) He can research in the direction of animagus transformation and Metamorphmagus, as a way to turn her into a full animagus, thus making it into a good thing, but he would need their help getting not only books on those subjects, or animagus and Metamorphmagus volunteers to study them, but also to find other people like Astoria, and even some who might have already fully turned, making it the most expensive of them all, as even polyjuice, if you want big quantities, you can just raise the ingredients at home, and they would only need the transfiguration master's help for a few years, only until Daphne or even Astoria has good enough control to do it themselves.
Yet there was no question.
"We would get you everything you need just make her better."
This is the day that would change the life of a family of three.
This is the day that would lead to the greatest experimentation in the wizards world for the last 200 years.