The new, quiet rhythm of their work was a delicate thing. It was built on shared looks over floating parchments, on the easy exchange of a quill, on conversations that started with magical theory and drifted into… everything else. They were building a new foundation, and Hermione was terrified of putting a foot wrong.
It was during one of these sessions, a week after her return to the chamber, that the first thread came loose.
They were debating the ethical implications of leaving a Sentient Magical Memorial Site completely unattended when Cassian, without looking up from a runic sequence, asked, "What did Weasley think of our report?"
The question was so casual, so utterly out of the blue, that it took Hermione a moment to process it. "Ron? Why would he… I didn't discuss the specifics with him. It's classified."
Cassian made a non-committal sound, his quill still moving. "He just seems… invested."
"He's a friend. A protective one. It's his nature." She tried to keep her voice light, but a defensive note had crept in.
"I'm sure." He finally looked up, his expression unreadable. "And the good-hearted, protective friend is now dating the brilliant, beautiful Ravenclaw. A very… neat resolution."
Hermione froze. The air in the chamber, which had felt so warm and collaborative moments before, turned icy. He said it so calmly, but the words were laced with something sharp and acidic. It wasn't just an observation. It was a judgment.
"What is that supposed to mean?" she asked, her voice dangerously quiet.
He put his quill down with deliberate slowness. "It means it's a very tidy ending for him, isn't it? The war hero gets the girl. Or in this case, a different, equally suitable girl. No messy feelings. No complications. Everything back in its proper, orderly place."
He was looking at her now, his gaze intense and challenging. He wasn't talking about Ron. He was talking about her. He was accusing her of wanting the same thing—a tidy, orderly life, free from complications. Free from him.
The accusation, so close to the fears she'd been wrestling with herself, felt like a physical slap.
"You have no right," she whispered, her hands trembling. "You have no right to talk about my friends, or my life, like that. You don't know anything about it."
"Don't I?" he shot back, standing up, his chair scraping harshly against the stone. "I've seen how you operate, Granger. You build foundations. You create order out of chaos. You file away dangerous, messy things in reports so you don't have to feel them anymore. Is that what you're doing now? Filing me away as an 'adequate' colleague? A contained, professional complication?"
He was voicing her deepest insecurities, throwing them back in her face with a brutal accuracy that stole her breath. The fragile trust they had built was unraveling before her eyes, torn apart by a bitterness she didn't understand.
"That's not fair," she said, her voice rising. "After everything we've been through together, how can you think that of me?"
"Because I see the way you look at me sometimes!" he retorted, his own control snapping. The words echoed in the small chamber, raw and unfiltered. "Like I'm a problem you haven't quite solved yet. A variable in your equation that won't balance. You're so busy trying to fit everything into your perfectly organized world that you can't see what's right in front of you!"
"And what is that, Cassian?" she demanded, standing to face him, tears of frustration and hurt stinging her eyes. "What is right in front of me? An arrogant, condescending man who pushes everyone away and then gets angry when they don't fight hard enough to stay!"
The moment the words left her mouth, she regretted them. His face went blank, all the anger draining away to be replaced by a cold, distant mask. It was worse than his fury. It was a complete and total withdrawal.
"You're right," he said, his voice flat and hollow. "That's exactly what I am. My apologies for the… complication."
He turned, gathered his cloak in one swift movement, and walked out of the chamber. The door swung shut behind him with a soft, final click.
Hermione stood alone in the humming silence, the echo of their fight ringing in her ears. The warmth was gone. The easy camaraderie was shattered. She had accused him of being a complication, and he had agreed.
She looked at the Vault, its dark surface swirling impassively. It had witnessed their collaboration, their shared trauma, their fragile connection. And now it had witnessed this—the violent unravelling of it all.
He had seen right through her. He had seen her fear of the messy, unpredictable feelings he stirred in her. And in her panic, she had confirmed his worst assumptions.
She had been trying so hard to build a new foundation with him, and with one careless, cruel sentence, she had blown it to pieces. The chaos was back. But this time, it wasn't a magical mystery in a dungeon. It was the devastating, self-inflicted chaos of a heart she had no idea how to fix.