While the trio of girls was lost in the theoretical complexities of magical reactors and solar conversion runes, Harry was facing a far more visceral and immediate threat. The connection between his mind and Lord Voldemort's, forged on the night his parents died, was strengthening.
It began as flashes in his dreams—dark corridors, hushed, sibilant whispers, and a cold, coiling sense of triumphant malice. Then, the visions started bleeding into his waking hours. During a particularly dull History of Magic lecture, the classroom dissolved for a moment, and he found himself looking through another's eyes, staring at a gnarled, white wand held in a long, pale hand. He came back to himself with a gasp, his scar burning like fire.
He confessed what was happening to Sirius and Remus via the two-way mirror Sirius had given him as a gift. The response was swift and grave. Dumbledore was informed, and a decision was made. Harry needed to learn to shield his mind. He needed Occlumency.
The news of who his teacher would be was delivered by Dumbledore himself, and it landed like a lead weight in Harry's stomach.
"Professor Snape, Harry, is a supremely accomplished Occlumens," Dumbledore had explained, his expression leaving no room for argument. "He has defended his mind against the most powerful Legilimens in history. There is no one better qualified to teach you."
The lessons were, from the very beginning, a disaster. They took place in the gloomy, dungeon office, the air thick with Snape's animosity. There was no instruction, no guidance. Snape simply ordered Harry to empty his mind, and then, with a vicious "Legilimens!", he would launch a fullscale assault on Harry's consciousness.
Harry was overwhelmed. His most private, painful, and humiliating memories were ripped from him and laid bare for his most hated professor to sneer at—the cupboard under the stairs, Marge's insults, his terror in the graveyard. He would try to fight back, but his anger and fear only made his mind more vulnerable. Each lesson left him exhausted, furious, and with a searing headache. After two weeks of this nightly torment, he was making no progress. He was just being psychologically flayed, over and over again.
Desperate, he sought out Ariana. He found her, as usual, in the library, a complex diagram of what looked like a runic power-converter spread out before her.
"Ariana," he said, his voice low and strained. "I need to talk to you. About the Occlumency lessons."
She looked up, her analytical gaze immediately taking in his pale face, the dark circles under his eyes, and the tension in his posture. "The sessions are not proceeding logically," she stated, not as a question.
"They're a nightmare," Harry confessed, slumping into the chair opposite her. "He's not teaching me anything. He's just… attacking me. He enjoys seeing me fail. I can't learn like this. I was wondering… could you teach me instead? You know about all this mind-magic stuff. You could show me how to do it right."
It was a plea from a desperate friend, an appeal to the person whose competence and power he trusted above all others. He expected her to agree immediately, to devise a logical, efficient training regimen that would have him shielding his mind in days.
Her answer shocked him.
"No, Harry," she said, her voice calm and absolute.
He stared at her, speechless. "No? But… why not?"
"Because my approach would not be effective for the threat you are facing," she explained, her tone that of a strategist discussing military doctrine. "I could teach you the theory of Occlumency. I could guide you through the meditative states required to order your thoughts and build mental walls. My method would be calm, logical, and based on mutual respect. It would, in time, be successful."
She paused, her gaze becoming intense. "And it would leave you completely defenseless."
"What?" Harry stammered. "How?"
"You are training to defend your mind against Lord Voldemort," she stated, the name spoken with a clinical lack of fear. "He is not a logical or respectful opponent. When he attacks your mind, he will not do so in a calm, controlled environment. He will do so when you are tired, when you are angry, when you are afraid. He will use your emotions as a weapon against you. He will rip and tear at your consciousness with pure, sadistic malice."
She leaned forward, her voice dropping but losing none of its intensity. "My gentle, logical method would teach you how to build a fortress on peaceful ground. It would be a beautiful, well-ordered fortress, but it would have no experience of being under siege. It would crumble at the first real assault."
"So you're saying Snape torturing me is… good?" Harry asked, his voice full of disbelief.
"I am saying that Professor Snape's method, while crude, aggressive, and fueled by his personal animosity, is a perfect simulation of the enemy you will actually face," she corrected. "He is attacking you when you are angry and resentful. He is using your own emotional turmoil to breach your defenses. He is, unintentionally, the perfect sparring partner. He is teaching you how to build your fortress in the middle of a battlefield, under constant, relentless fire."
The cold, hard logic of it was brutal, but it was also undeniable. Harry had been seeing the lessons as a personal torment. Ariana saw them as a stress test, a live-fire exercise.
"You believe you are failing because you cannot empty your mind," she continued. "That is Snape's flawed instruction. Your strength is not emptiness, Harry. Your strength is your emotion. Your love for your friends, your grief for your parents, your righteous anger at injustice. You cannot empty your mind of these things. To do so would be to cease being you."
"So what do I do?" he pleaded.
"You do not build an empty fortress. You build a citadel around what you value most," she said. "You learn to use your emotions not as a weakness, but as a shield. When he attacks, do not try to block him with nothing. Focus on a single, powerful, positive memory—your first flight on a broom, seeing Hogwarts for the first time, the feeling of your family standing with you at the World Cup. Use the raw power of that emotion to build a wall of light that sears him on contact. Fight his hatred with your love. That is a battle he can never win."
She had not offered to replace his teacher. She had not offered him an easy way out. She had, instead, given him a new strategy. She had reframed his perceived weakness as his greatest strength.
Harry looked at her, at his brilliant, sometimes terrifyingly logical friend. She was right. It was a harsh, painful truth, but it was the truth. Snape's lessons were hell, but they were a necessary hell. He had to learn to fight in the dark, not just in the light.
"Okay," he said, a new, grim determination settling over him. "Okay. I understand."
He would go back to the dungeons. He would face Snape's attacks. But this time, he wouldn't be trying to be empty. He would be armed with the memories of his friends, his family, and his own joy. He would learn to fight like himself. And that, he realized, was a lesson only a teacher as harsh as Snape, and a friend as logical as Ariana, could have taught him.