The six levels of espers in Academy City range from Level 0 espers, who have no power at all, to Level 5 espers, who are practically invincible and at the top of the food chain. Only seven Espers have, so yet, attained Level 5, with Accelerator being the most powerful of them. The main character of Kazuma Kamachi's Toaru Majutsu no Index Gaiden: To Aru Kagaku no Ippou Tsuukou: To Aru Kagaku no Ippou Tsuukou anime adaptation, A Certain Scientific Accelerator, is the strongest Level 5 Esper who has had to give up a lot of his power after saving the contented little Last Order.
So while Accelerator is in the hospital rebuilding his health, he has a reasonably tranquil life until he saves the life of a stranger, Esther Rosenthal, who is holding a picture of Last Order. It turns out that Last Order is being sought after by the evil group Disciplinary Action, who plan to exploit her for a perilous mission. It is once more up to Accelerator to look out for his young pal while also saving Academy City because Disciplinary Action is already hot on Last Order's tail. However, he is not entirely alone this time.
