Certain Magical Index NT, Vol. 2 (light novel)

Danger Overhead... As the dust settles from their encounter with the Freshmen, Touma Kamijou, Shiage Hamazura, and Accelerator finally cross paths in Academy City. Before long, these three find themselves with yet another challenge on their hands-explaining what the heck they've been doing to everyone who was worried about them! Amid this series of reunions, Birdway gives Kamijou and the others a crash course on the fundamentals of magic and warns them about a new threat that has emerged from the ashes of World War III. Meanwhile, Kanzaki takes to the skies on behalf of Necessarius to investigate a floating fortress...and discovers that it's set to collide with Academy City! Can the worlds of science and magic coordinate in time to prevent disaster?