We're not really Doctors. (Shirou x Harem) Arknights x Fate

Chapter 25 - 2

"Trace On."

Shirou needed something powerful. Something to threaten Talulah with. Death wasn't an option, so he had to settle for something...crippling instead. For someone who relied so much on fire magic, nothing could be worse than taking away their magic.

A shape formed in the air in front of him, drawing a significant chunk of energy from Shirou. It would be worth it, as the object also doubled as a form of defense to keep Talulah in check later down the line.

A black handle appeared, slowly followed by the purple shimmering jagged blade connected to it. A small noble phantasm Shirou personally witnessed during the 5th Holy Grail War. The noble phantasm of a famous Witch of Betrayal, the manifestation of her legend.

Rule Breaker, it who invalidates all magic. The ultimate anti-magic Noble Phantasm capable of dispelling and destroying all kinds of magic.

A dagger that nullifies all effects created by magic, despite whether such an effect is an enchantment, a relationship formed through contact, or even life created through magical energy.

All parties narrowed their eyes at the object Shirou materialized. The dagger's shape was odd. It had no practical design, looking like some weird trinket instead of a weapon it was shaped after.

"Your plan is to cut me?" Talulah drawled. "You could kill me and I still wouldn't talk."

Suddenly, the chains around her broke. Talulah didn't question the opportunity and scrambled to her feet.

"This dagger is made for rituals. Not just to cast them, but to end them." Shirou raised the dagger in front of her. "It can take away your arts...for good. This dagger has destroyed magic far older and stronger than yours. So I'll give you an opportunity to tell me where the key is before I cut you with this."

Shirou could feel Patriot's stare weigh heavily behind him. He had just released Talulah after all. She was back on her feet with a guarded stance facing him.

The air shimmered as a wave of heat erupted from Talulah's hands. The fireball shot at Shirou, only to extinguish by receiving it with Rule Breaker. It dispersed upon contact with the dagger in front of all parties. The dragon stared hard at the weapon with scrutiny and a little bit of hesitation.

"It's your choice."

"Hmph-" Talulah chuckled. "And what do you think that will do? We're all dying when Chernobog hits Lungmen. Cripple me if you want, your threat means nothing."

Shirou didn't bother wasting time. He dashed in, nullified a weak fireball attempt from Talulah, then lightly cut her on the arm before she could draw away. She didn't bother putting much effort into it, already confident with her victory.

The leader of the Reunion collapsed to her knees in front of him, drawing some suspicion from Shirou. Getting cut by Rule Breaker didn't physically affect a target outside of small superficial damage. Rather, it was the sudden loss of the connection to magic that the victim felt. Perhaps she fell from the jarring sensation? He wasn't sure.

If threats didn't work, then Shirou had another option.

Binding contracts.

Years spent studying the Holy Grail in his possession in combination with Sakura and Rin's expertise helped boost their own understanding of contracts. While not on the level of Zouken Matou who created the contract system, it was still a significant chunk of knowledge.

Rule Breaker's primary effect was to break magic, up to and including magical contracts. Still, the ritual dagger was made for rituals- able to perform esoteric magic counter to its essence. In combination with the Holy Grail within Shirou and his own takeaways from years of research, he had the necessary tools to establish a binding contract.