Immortal Regiment

The Immortal Regiment or Undead Regiment is a  owned by Ōgai Mori.

Description
No specific information is known other than it is a classified data.

However it is heavily implied that the intent was to create an immortal, unceasing army. Using the unique ability of Akiko Yosono that could heal injury, excluding death itself, and return a soldier to perfect condition the Immortal Regiment would be an army that would never need to retreat. Regardless of another army's might the unit would overwhelm them as they could fight infinitely while any other army would inevitably run out of soldiers and resources.

While good in theory it failed to take into account the human element and failed terribly. Yosono's ability only worked if the patient was on the brink of the death, if the soldier merely had a broken arm they would have to be severely injured further. As sending soldiers home for minor injuries or letting them take time to heal mentally would defeat the purpose of a true immortal army, the ruthless Mori kept all soldiers on the battlefield, critically wounding them himself in order to get them healed. As a result of the endless cycle of being brought to the brink of death only to be healed and sent right out again destroyed the unit mentally, including Akiko Yosono who went so far as to try and bomb the carrier to end the project.

The failure of the Immortal Regiment due the psychological effects of likely led to the creation of One Order. An inverse of the Immortal Regiment that sought to create the perfect army by fixing physical limitations, One Order worked by fixing mental limitations; Once activated soldiers would mindlessly obey orders in a trance like state where they would not register any of their actions and not remember anything once One Order was deactivated. This would rob the soldiers of free will but would protect them from the psychological effects of war.

Yosano's ability was used by Mori in order for the skill doctrine to be proven its worth to the upper brass during the Great War. Moreover, three years after the war, Mori believes that an "Immortal Regiment" led by Yosano is capable of taking down the Port Mafia boss who is causing violence and havoc to the city, stating that she is a keystone in maintaining the Tripartite Framework.