Awakening

Awakening (覚醒) is the term used when an esper develops a completely new level of power, manifesting angelic characteristics, such as wings and a halo. So far, only Accelerator and Kakine Teitoku, the two most powerful espers in Academy City, have been shown to be able to Awaken.

Kamijou Touma's 'awakening' refers not to the angelic nature that Kakine and Accelerator is capable of, but to the awakening of Imagine Breaker and/or some other existence inside of him; as demonstrated in Touma's fight against Fiamma of the Right on the Star of Bethlehem

Index witnessed Accelerator's first incomplete awakening while he was fighting Kihara Amata, and 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. She also claimed that while the nature of the power was similar to Telesma, it was also fundamentally different in some way.

The "awakening" process itself is actually quite simple yet not easily achieved. The esper must have an important revelation; a realization important enough to have an influence in the way the user lives his life. Since the usage of powers is related to personality, the awakening process might be described as similar to "maturing" or "growing up" mentally. Both Kakine and Accelerator have shown that based on the type of revelation, the power gained can be completely different.

Kakine first awakening gave him 3 pairs of wings, when Kakine had a better revelation the wings increased in size tremendously while keeping their original shape. The basis of Kakine's awakening was revealed to be "Understanding of how esper powers work" and "where they come from".

The Accelerator's first awakening gave him huge black wings which he is able to utilize as blades. However, when Accelerator changes his way of thinking, his black devilish wings become completely white and he also gains a halo as well. The basis of Accelerator's awakening was revealed to be related to the determination he has when "fighting between life or death" as well of his own stance about "killing or not killing" his enemy.

Trivia

 * Index referrers to her John's Pen Mode activation as Awakening, however she uses a different reading for the Kanji ( Awakening (覚醒める) ). John's Pen Mode itself also uses the term "Awakening" for it's activation. . It should be noted that the most natural writing for "mezameru" in that case is 目覚める (Mezameru), and thus 覚醒 (Kakusei) is forcibly used by the author. It should be noted that John's Pen Mode also displays wings.
 * So far, all "awakened" espers take on forms resembling angels, whether this is the case for all "awakenings" is unknown, due to those having the potential to "awaken" being so few.