Coronzon Arc

The Coronzon Arc is a major story arc in Shinyaku Toaru Majutsu no Index, culminating major events built up throughout the entire novel series, covered in Shinyaku Toaru Majutsu no Index Volume 20 and Volume 21.

With Coronzon temporarily sealed in the evacuated Academy City, Kamijou Touma, Accelerator, Hamazura Shiage and a number of their allies accompany Aleister Crowley to the United Kingdom, currently under attack, in order to find the Great Demon's achilles heel before she breaks free once more. However, the demon's machinations have left many adversaries, obstacles and traps in their path.

Trivia

 * Despite this being a "multi-part" story arc, Kamachi even noting this in Volume 21's Afterword, the chapter number resets back to 1 between volumes, as it would for a standalone volume. The reasons for this are unknown.