Harry was reading her book on light and dark magic one day in the summer, whilst Draco was out at a social even with his father, when she found something that made her sit up and gasp. She quickly put her bookmark in before jumping up and beginning to pace back and forth, her mind whirring. About 20 minutes later, she sat back down and picked up the book again, checking the chapter index at the front before flipping to the very back of the book. She walked over to her blackboard - she had asked Draco for it at Easter - and began to copy down the runes shown in the text. And that was how Draco found her the next morning, half-asleep and with a blackboard full of runes.
Ignoring all her protests that she had something important to tell him, he guided her to her bed and gently lay her down on it. She fell asleep instantly.
When Harry awoke seven hours later, she found Draco sitting on the armchair opposite the one she always sat in, reading a book on magic-based illnesses. When he saw that she was awake, Draco left the book on the small table by his chair, and walked over to where Harry had jumped out of bed to.
"Draco, I found something really important! I need to tell you!" She shouted, extremely excited.
"Harry! Just because you're excited, it doesn't mean that you can neglect to sleep." Draco replied, clearly worried.
"Not right now, little dragon." Harry said back absentmindedly.
"So, I was reading my book on light and dark magic, when I saw this:" and Harry began to read it out.
"Almost every wizard or witch has a magical alignment: light or dark. Contrary to common belief, light does not mean good, nor does dark mean evil. However, a wizard or witch who has a light alignment will struggle to use light spells, and vice versa. To learn how to use spells of the opposite alignement to your own effectively, turn to the chapter on use."
"See, Draco?" Harry exclaimed, turning to Draco, who seemed to think for a few seconds before gasping loudly.
"I have a dark core?!" He shouted, excited that he finally knew what was wrong with him.
"That's the conclusion I came to, too. But there is a way we can check; the last chapter in the book has a ritual that we can perform to be able to see magical alignment; that's what I was writing down last night." Harry said, ignoring Draco's muttered "and this morning."
o - o - o - o - o
By the next day, Harry and Draco had both learnt the runes well enough for them to perform the ritual. They had discovered that you had to perform the ritual on yourself, but they decided to go one at a time, in case anything went wrong.
Draco went first, and he pulled his wand out and began to trace the runes in the air, copying them off the blackboard. Each rune he traced glowed a silver colur before fading away, but the last rune he drew stayed there for a few seconds before moving towards him and settling on his collarbone. It once again flowed silver before fading to black. Draco turned and flared at Harry.
"You didn't say I'd get a tattoo! My mother is going to kill me." he groaned, glaring at the black rune tattooed on his shoulder.
"Where is your mother? I'd have thought I'd have seen her by now." Harry commented, curious.
"She's been staying with some distant relatives for the past year, and only got back yesterday." Draco responded, turning around. As soon as his eyes met Harry, his scowl at the tattoo quickly morphed into a look of wonderment.
"Your magic..." Draco was left speechless.
Draco could see Harry's magic pulsing against her skin, a shining silver.
He stared at her for a few seconds before Harry grew bored, and turned around to begin her own ritual. Instead of wand, she traced the runes with her finger, but apart from that the ritual was exactly the same. Once again, the marks in the air glowed a bright silver before fading away, except the last mark; like with Draco, it pressed itself against her collarbone and faded to black. Harry glanced at it, before turning around to face Draco; she is just as awestruck by the sight of his magic as he was hers: his whole body seemed to thrum with dark power, faint wisps floating out into the surrounding air. The sight seemed to give her an idea, and she thought for a second before speaking.
"Draco, why don't we let our magic out? We might be able to see it." Harry said, and then they both released their magic; immediately, they both gasped. Their magic wove together, dancing through the room and saturating the air with black and silver. After what felt to them like only minutes, but what was actually longer, Harry suddenly exclaimed "Draco! We were right, your magical alignment is dark; that's why you struggle so much with Hogwarts' light spells", finally remembering why they did the ritual in the first place.
"I'm happy to have finally found out why I struggle so much with some spells, but it doesn't give us a solution." Draco frowned.
"I don't know" Harry responded, also frowning, before saying "but the book does have a chapter on that. If you give me a few days, I'll find out for you." And with that, Harry went and curled up with her book, pulling her magic back into her body and tucking some of her raven hair behind her ears.
Draco went over to Harry's desk, where his stack of school textbooks was, and began his holiday homework.
o - o - o - o - o
Five hours later, Draco had finished his charms essay. He stretched, before glancing over to where Harry hadn't moved an inch. He sighed; she would probably be like that for at least a day. With that thought, Draco headed out of Harry's room and downstairs to the dining hall, to eat dinner with his father and mother.
When he reached the dining hall, his mother looked up at him, confused.
"It is unlike you to be late, Draco, darling. Where were you?" She asked, unaware that the girl-who-lived was staying; she'd only been back for a day, after all, and Lucius wasn't sure how to break the news to her.
"I was doing my homework and lost track of time" Draco answered truthfully, but he could see his father raise an eyebrow at his son's words.
They ate mostly in silence, only broken by the occasional polite conversation. Before Draco was allowed to leave the table, however, Narcissa started a conversation again.
"Draco, dearest, I'll be busy tomorrow, but can I spend some time with you the morning after that?" She asked, wanting to catch up with her only son after being away for almost a year.
"Um... I might be busy, mother." Draco replied, unsure of whether his father had told his mother about Harry yet.
By her responding look of confusion, and his fathers slight shake of his head, Draco realised that his father was still building up the courage to ask his - sometimes terrifying - mother.
"What could you possibly be doing that can't be postponed?" Narcissa asked, incredulous.
"I'll try to be free." Draco replied, dodging the question.