The large-scale offensive work began with theory, because it always began with theory — the specific practice of understanding what a thing was before attempting to do the thing.
He had spent considerable time over the previous year identifying the gap between dueling magic and field magic, which was not a gap most Hogwarts curricula acknowledged. Dueling was person-to-person: a controlled exchange between two parties with defined positions and a clear target. Field magic was something else entirely — the management of multiple targets at different distances, the specific challenge of spells that needed to function across open ground rather than across a dueling circle, the particular discipline of someone who needed to affect a space rather than a specific individual within it.
'Confinement first,' he said, on the first Monday session. 'The principle of binding a space rather than a person. You're not trying to hit someone — you're trying to make a section of ground one that no one can leave.'
He demonstrated. The binding field expanded from his wand with the specific quality of contained effort — not the aggressive release of a combat spell but the sustained output of something that needed to hold rather than strike. It covered perhaps fifteen square feet, visible as a faint shimmer at its edges, and when Neville tested it from inside by attempting a simple Summoning Charm, the charm failed.
'It dampens offensive magic within the field,' Ron said. 'It won't stop someone from walking out of it. The point is to combine it with something that does.'
He held the field for ninety seconds and then released it.
He was aware, as he always was after sustained high-output magic, of the specific quality of the effort — the slight depletion that was not exhaustion but was adjacent to it, the particular sensation of having drawn on a reserve and needing to let it replenish. He had been managing this awareness since the Room of Requirements in second year and had learned to treat it as information rather than alarm: a gauge, not a warning.
'That took something from you,' Hermione said. Not an accusation — an observation, precise and careful.
'Yes,' he said. 'High-sustained-output magic costs more than point-and-release work. This is the principle behind field magic — it requires more, and the more it requires, the longer it needs to hold. The gap between what it costs and what you can sustain is what you're building over the next few months.'
Harry was looking at him with the quality he had when he was storing something as specifically important. 'Is there a limit?'
'For everyone,' Ron said. 'Mine is higher than most people's. Yours is higher than you know yet. We are going to find out where it is in conditions where finding out doesn't matter — so that in conditions where it matters, you already know.'
The ward work was different in quality and required different preparation.
He had been studying wards since third year — the theoretical framework was Ancient Runes territory, which was one of the reasons he had taken Runes and pushed into the advanced material as quickly as he had. The practical application was something he had been developing in parallel: the specific skill of reading a ward without triggering it, understanding its architecture from outside, identifying the structural points that held it together.
'Every ward has a keystone,' he said, on the Thursday of the second week. 'A point in the runic structure where the whole thing is anchored. Find the keystone and you can either dismantle the ward from there, redirect it, or pass through the gap that dismantling creates without the ward registering the passage.'
He had constructed a practice ward in the Room — a simple one, designed to be read rather than to genuinely exclude — and he walked them through the diagnostic process. The wand at rest, not casting, held in the specific loose configuration that allowed it to receive rather than transmit. The breath slowed. The attention extended outward rather than focused.
'You're listening,' he said. 'Not looking. Wards are not visual. They have a frequency. When you can feel the frequency you can find where it comes from.'
Luna, predictably, found the keystone first.
She had her wand held in exactly the position he had described and was moving it slowly along the ward's perimeter with the quality she brought to things she was genuinely attending to, and she stopped at a point perhaps four feet from the left edge and said, quietly: 'Here.'
He checked. She was correct.
'How did you do that,' Harry said.
'It sounds different there,' Luna said. 'Lower. Like a note that's working harder than the others.'
He filed this alongside the stealth work and the natural stillness. Luna Lovegood's specific relationship with magical perception was not a thing the standard curriculum had a framework for. He was developing one.
He taught the targeted curse work in the third week, which was when he had judged the group was ready for it — not technically, but in the specific sense of having built enough context that the material would land as part of a larger picture rather than as something isolated and alarming.
He was direct about what he was teaching.
'These spells are designed to end a confrontation quickly,' he said. 'Some of them are painful. Some of them will cause lasting damage if applied incorrectly or held too long. I am teaching them to you because the alternative — encountering a situation that requires them without knowing how to use them — is worse than the discomfort of knowing.' He looked at them steadily. 'You are not going to become different people because you know how these work. Knowledge is not the same as use. But I need you to understand both.'
The spells he chose were specific: three disabling curses that functioned at range, designed to drop a target without requiring sustained contact; two that worked on the specific physiology of dark creatures — the silver-based variant for werewolves that he had developed from Runes theory over the summer, targeting the transformation mechanism rather than the individual; and one that he did not teach from his wand but from a diagram, because it was the kind of spell that was better understood as a concept before it was understood as a cast.
Hermione looked at the diagram for a long time.
'This would stop someone permanently,' she said.
'Yes,' he said.
'You're teaching us to kill people.'
'I'm teaching you that it is possible,' he said. 'And what it costs. And why it is the last option, not the first, not the second, not the fifth.' He held her gaze. 'In a war there are situations where the choice is between your life and someone else's, and the person who has never thought about that before is the one who freezes. I am not asking you to become someone who kills easily. I am asking you to be someone who, if it comes to that, has already decided what they would do and why.'
A long silence.
'Okay,' Harry said. Simply. With the quality of someone for whom this had been a real and present consideration for longer than anyone in the room except Ron knew.
The others followed, each in their own register. Hermione last, and her yes had the quality of the hardest kind of yes — the one that had looked at all of the available alternatives and found them wanting.
He put the diagram away.
'We won't practice the last one,' he said. 'Not the casting. The rest we will practice until it is clean and fast and you could do it in the dark.' He looked around at them. 'Now. We're going to talk about giants.'
Neville made a sound that was not quite a laugh.
'I know,' Ron said. 'But we need to.'