Awakening

Awakening is the term used when an esper develops a completely new level of power, often manifesting in angelic characteristics, such as wings and, in Accelerator's case, a halo. Not every esper has the potential to awaken, in fact the only ones to have achieved this were the top two espers of Academy City, Kakine Teitoku and Accelerator, although it has been hinted that Kamijou Touma has the potential to awaken.

Index withnessed Accelerator's first incomplete awakening while he was fighting Kihara Amata, and shockedly she thought to herself that the power he used then was so great, that not even a saint would have been able to handle it.