The 6th volume in the Uragiri wa Boku no Namae o Shitteiru series.
When Shuusei and Tooko drop off the radar while on a special mission to Kyoto, concern for their safety reaches a fever pitch at Twilight Hall. While preparing to rush to their rescue, Yuki and company are relieved to hear word that Tooko has been found. Still, with no word from Shuusei, a party heads to Kyoto to locate their ally. But while they're away, the suspicious deaths around the city are confirmed to be the work of the Duras. Will the remaining Zweilt be able to confront the enemy and save the innocent with their forces so severely depleted?!