“Protego Diabolica!” Harry tried, waving Sirius’ wand. Black fire formed, if only for a moment. Like a flame without fuel it sputtered out, fading away into the wind.

“That won’t work, Harry, you have to mean it.” Sirius said.

“I know I’m not a mean person, if that’s what you mean.” Harry said.

Sirius gave him a sideways look. “Really, Harry? I would expect better from Lily’s son. Bad jokes aside, that wasn’t what I meant. The dark arts require intention, more so than regular spells, do you get what I mean?” He asked.

Harry shook his head. Sirius frowned. “Perhaps I’ve explained it poorly. The dark arts require malicious intent. A strong intent to kill or cause harm. It makes spells like the killing curse function. Here, let me show you.” Sirius said, grabbing his wand.

He pointed it at Harry’s head. “Crucio!” He shouted. Harry stared at his godfather blankly.

“Was that a joke?” He asked.

“The unforgivable curses are hardly the type of thing to joke around with, Harry. You saw me say the words, point my wand. But the spell failed, can you tell me why?” He asked.

“Because you never hit me with anything, I didn’t see a spell.” Harry said.

Sirius shook his head. “No, no, that’s not right. I have a better example. Avada Kedavra!” He shouted, pointing his wand high up into the sky. A green light flashed, and a bird fell to the ground, it’s blood splattering on the stone of the garden.

Sirius turned around, his wand pointed towards Harry’s face. “Avada Kedavra!” He shouted. Harry yelped, and tried to dodge, but the light was too fast. It headed for him, streaking through the air to strike his chest. He fell to the ground. But nothing happened.

“What?” Harry asked, scrambling back up.

“Now.” Sirius said, his face a mask of patience. “What happened there?” He asked.

Harry tapped his lightning scar. “You didn’t have the intent to kill me, so you didn’t?” He asked.

Sirius nodded. “Very good, Harry.”

“So that’s what the dark arts are about. You need to hate, want to cause harm.” Harry realized.

“Is that why they are forbidden?”

Sirius nodded again. “Precisely. The dark arts require malicious intent, a drive to hurt and to kill. They are, in reality, not much different from normal magic, and can be used for a lot of good. Yet, using them requires strong emotions, which almost never results in anything desirable. Few wizards can master the power of the dark arts while fending off the taint of it’s corruption.” He explained.

“Few? So there are those who can?” Harry asked, his eyes gleaming.

Sirius frowned. “Not exactly. The most powerful of dark wizards learn to control their emotions, summoning burning rage and chilling indifference as they see fit. They master their thoughts, control every action, but… not many are what you would consider human. They are like bodies without a soul, unable to laugh, unable to feel. Strange things happen to a person’s mind when they learn to separate their minds from the events of the world. They are like immovable stones in an ever flowing river, uncaring and out of place.” Sirius said.

“Who?” Harry demanded.

Sirius pondered it for a moment. “I cannot say if Voldemort has any emotion, if he does, he rarely shows it and I have not seen it. But there may be a better example, Grindelwald. Of all those who dabble in the dark arts he is the most skilled by far, so much so that he could summon anger for a spell just as I could summon water. Then he could stamp out any emotion if he deems necessary less than a second later. If I were to describe him, I would call his control inhuman.” He said.

Harry looked up at him. “But, if they are all really so heartless? Why do they even live?”

Sirius looked at him in surprise. “A good question, Harry. I’m afraid I can’t answer. I believe there are books on the subject, how to retain some measure of humanity while having complete control of the dark arts.” He paused, seeing the flash in Harry’s eyes. “However, most are in the restricted section of Hogwarts libraries, and even Durmstrang would expel most students for looking into it without permission. I suspect it has something to do with old magic, the most primal and terrible.”

He sighed. “If my advice means anything, try not to dwell on this type of magic too much. It’s like a hungry beast, ever insatiable and constantly devouring the souls of whoever it can find, eating away at their minds until what’s left is no better than itself. I taught you so that you could defend yourself against death eaters, don’t use these spells unless you must.”

Harry nodded. “I won’t.” He said, surprised he meant it.

“I expect you to keep that promise, Harry. Now, you’ve been a good student, and I must say I’m rather sad to see you leave, but you have done well, better than I could have dreamed. Now, don’t drop your head like that, we can always meet for dinner one Sunday or another. Anyhow, I wish I could teach you more, but if Voldemort is truly running loose then lessons on pranks will do very little good. Here, give this letter to your mother. Consider it a birthday gift from your godfather.” Sirius said, handing him a sealed parchment.

“Birthday present?” Harry asked, feeling some excitement.

Sirius chuckled, his smile teeming with mystery. “You will see, Harry. I’m sure it won’t disappoint.”