The Cruciatus Curse is actually a spell that is easy to learn but difficult to master. Among the three Unforgivable Curses, the only one that truly requires technical skill is the Imperius Curse.
As long as someone knows the incantation and understands a bit of the casting principles, even a student who has only studied magic for a few years can cast the Cruciatus Curse and the Killing Curse.
Of course, the actual effect is often weaker than even ordinary spells.
Draco and Neville were slightly beyond that stage.
If they truly harbored malicious intent and genuinely wanted to cast it, they could produce the full effect of the Cruciatus Curse.
However, Tver had never taught them this spell so they could use it to torture others.
When it came to inflicting pain, it was not that he looked down on the Cruciatus Curse. He knew plenty of white magic that worked even better.
There was simply no need to risk being discovered or to let one's mind be corroded just to use an Unforgivable Curse.
If corruption was inevitable, then one might as well use stronger and more effective dark magic.
This was a philosophy Grindelwald had passed on to him, and he had, in turn, passed it on to Percy and the others who studied under him.
So once Draco and Neville had learned the Cruciatus Curse, Tver no longer allowed them to practice it on each other, nor did he permit them to use it on anyone else.
Instead, he began guiding them to understand how the spell worked, helping them grasp how it bypassed the body and directly tormented the soul.
This was the most difficult part of learning the Cruciatus Curse.
Most dark wizards never studied it at this level. Only those who sought true mastery would think about such things.
Unfortunately, even Tver's own research in this area was not much more advanced than that of those who came before him.
In other words, throughout history, there had been little real progress in understanding this spell.
"I need to remind you that even I have not studied the Cruciatus Curse to this extent. In the lessons ahead, I won't be able to guide you step by step like before."
"I can only give you direction and help you avoid letting dark magic erode your minds as much as possible."
"But you must be prepared. The deeper you go, the more easily you will be influenced by the darkness within you."
"If you choose to stop, I will understand completely, and I can end your training at any time."
For Tver, the three Unforgivable Curses were forbidden territory. Even with his unmatched expertise in soul magic, he had not been able to unravel their true nature.
Hearing the seriousness in the professor's tone, Draco could not help but glance at Neville.
For him, as a pure-blood, studying dark magic was a straightforward matter.
But becoming a true dark wizard because of it was something neither he nor his parents could accept.
But Neville…
"I understand. I've always known that my purpose in learning the Cruciatus Curse was never to take revenge on Lestrange."
Neville's eyes were steady, his once timid expression now replaced with firm resolve.
"It's to better understand what happened to my parents, so I can help them recover."
"And," he added, turning to Draco, "Malfoy, I'm already grateful that you've stayed with me this long."
"So you don't have to keep going any further…"
"As if!" Draco clenched his teeth, his face flushing slightly.
"Don't think you can have the professor's lessons all to yourself. I won't let you!"
Tver glanced at Draco in surprise but said nothing, a faint smile of approval appearing on his face.
Among all the students he had taught, Draco's growth was one of the most striking.
From a practical standpoint, the time spent learning the Cruciatus Curse could have been used on far more rewarding subjects.
But for Neville, who already lacked companions, stopping here would mean returning to being alone.
If it were any other spell, it might not matter. But he was studying something as dark as the Cruciatus Curse.
Without someone to stand beside him, even with Tver watching over him, there was no guarantee Neville would not lose his way.
After all, a companion and a teacher serve very different roles.
"In that case, let's study and explore this together."
Tver took out a set of notes. They looked thin, but were extremely important.
"This is… well, research on the Cruciatus Curse done by a professional. You can start by reading through it."
This was the real reason he had contacted Marvolio today. Talking about Voldemort had only come up along the way.
After all, when it came to using the Cruciatus Curse, Marvolio was naturally more proficient than him.
"Of course, you don't need to look at the casting techniques inside," Tver quickly added when he saw the excitement on their faces.
Given how difficult it was to study the Cruciatus Curse, it was not something two students could handle.
He was simply using this opportunity to observe their reactions to the spell. The real research, and the only one truly capable of it, was still Tver himself.
Back when his strength had hit a bottleneck and he urgently needed to draw on the badge's power to extend his life, Tver had already considered researching the three Unforgivable Curses to break through his limits.
But the result had been clear. These spells involved the soul too deeply. Not only did he fail to make progress, he had nearly lost himself in the process.
Fortunately, that experience led him to Helga and set him on the four-year journey of finding the founders.
Now, however, he had gathered all the founders and fully awakened the badge's power. In Tver's estimation, he now held authority over Hogwarts that even surpassed Dumbledore as headmaster.
Under those circumstances, returning to the study of the Unforgivable Curses was only natural.
Especially since Voldemort had begun researching the soul earlier than him. He could not afford to fall behind.
However, after studying for an entire day, evening arrived. Professor McGonagall came to remind them to go to dinner and brought a message as well.
"Tver, remember to be at the Quidditch pitch at nine tonight… What are you two looking at?"
Professor McGonagall frowned at Draco and Neville, who were trying to hide what they were holding.
Neville, still terrible at lying, flushed bright red and could not get a word out. Draco was more composed, but even as excuses rose to his lips, he did not dare say them under her stern gaze.
"I'm teaching them the Cruciatus Curse."
Tver stood up casually, drained the last of his pumpkin juice, and gave Draco and Neville a subtle wink.
His calm attitude instead made Professor McGonagall drop the matter, though she shot him an annoyed look.
"Honestly, don't make jokes like that in front of students."
"Yes, yes, I won't next time. Come on, let's go eat."