Necromancer Arc

The Necromancer Arc (死霊術師編) is the first story arc of Toaru Kagaku no Accelerator. It deals with Disciplinary Action or DA, a rogue extremist group of Anti-Skill, and the parties manipulating them who make use of necromantic techniques.

Background
On August 31st, following the suspension of the Level 6 Shift Project after his defeat by Kamijou Touma, Accelerator was shot in the head by Amai Ao while saving Last Order. Although he was saved by Heaven Canceller, the brain damage he sustained left him reliant on the Sisters he had once killed, via a choker connecting him to the Misaka Network, in order to process language and perform calculations. During the first weeks of September, Accelerator remained an inpatient at Heaven Canceller's Hospital.

DA
Disciplinary Action, commonly abbreviated to DA, was an armed organization which began as a group of Anti-Skill officers who received disciplinary action for going overboard in their law enforcement. A cooperative organization on paper, it was actually a secret society of zealots and extremists, willing to use any means necessary to carry out what they call "justice". Comprised largely of disciplined and disgraced members of Anti-Skill, the group was supported by numerous sympathizers, including current and former members of Anti-Skill, certain influential figures and rejected defense contractors, supplying them with information, funding and equipment, with technology surpassing that of Anti-Skill. One of their backers was board member Nakimoto Rizou, who believed the group could be useful for him and kept that information on the group withheld from Anti-Skill.

Hishigata Mikihiko joined DA at some point within the past few years and provided them with the Coffin technology which he had developed from Esther Rosenthal's Necromancy techniques, though he merely planned to use the group for his own ends.

Three days before the incident at Heaven Canceller's Hospital,  several DA members came across Hitokawa Hasami after a failed suicide attempt and murdered her in the ambulance, drowning her with river water through her oxygen mask, in order to make use of her ability in the Prototype Coffin.