Spiral: The Bonds of Reasoning Vol 8

From the Yen Press edition

Despite thorough planning and preparation, the offensive against Kanon is not going well. Bruised and broken, Rio, Ryouko, and Kousuke are no closer to reaching Kanon than when they started. But Ayumu's trusty information-gathering sidekick is ready and willing to help out. Now they know where Kanon is holding the hapless Ayumu hostage, but they're still in no shape attack. Thankfully, Rio managed to nick Kanon with an anesthetic bullet in their last assault, so he too is taking time to recover. Now everyone's attention is on the mysterious representative of the "Watchers" who has arrived to hear Kanon's demands...

Source: Yen Press