Thou Shalt Not Die allows Yosano to heal all kinds of physical external injuries or any kind for herself and others with the one condition that they must have near fatal injuries. Therefore, in order for her ability to be used, the target must be injured enough to be half-dead.
Thou Shalt Not Die is often used as a means to heal the injuries of the Armed Detective Agency after combat, from which stems their maxim that receiving fatal injuries to the point of being barely alive is synonymous to having no injuries. One exception is Osamu Dazai, since No Longer Human actively nullifies any ability including Yosano's healing. This requires him to undergo standard medical procedure, such as surgery, to recover from external wounds that he receives.
It can also be used during direct combat, in which Yosano heals herself or others as they experience injuries. In some cases, Yosano uses her ability to satisfy her sadistic tendencies to the point that she tries to dissect those who have suffered minor injuries. In certain instances, Thou Shalt Not Die can be used for interrogation or torture purposes, in which Yosano heavily injures her opponent, heals them, and repeats the process until she is satisfied or gets the information she needs from them.
Though the ability is highly useful, it has some limitations. As Yosano once noted, if a target is too dismembered or blown to bits, her ability might not be able to heal them anymore. Her ability is also unable to heal internal injuries or illnesses. Moreover, Yosano is prone to exhaustion and fatigue if she overuses her ability, an example of which is when she once healed 80 people simultaneously in the past.
- Thou Shalt Not Die: Times Four (君死給勿・四連, Kimi Shinitamō Koto Nakare: Shiren?): Yosano is able to heal four people at once.
During the Great War, Yosano was recruited by then military physician Ōgai Mori primarily to use her ability for his Immortal Regiment strategy. This required Yosano to heal various war soldiers when they sustained injuries – some of which were life-threatening and psychologically traumatizing – to enable them to return to the battlefield. Though initially a game-changer during the war, the soldiers gradually turned against Yosano, believing that they were merely being healed to be attacked and nearly get killed over and over in the frontlines.
Three years after the war, Mori attempted to recruit Yosano for her ability once more in order to overthrow the erstwhile mafia boss, which Mori deemed to be for the benefit of maintaining the Tripartite Framework. However, Yukichi Fukuzawa and Ranpo Edogawa intervened, resulting to Mori's failure of earning Yosano's help in his scheme and her eventual entrance to the Agency upon Ranpo's recommendation.
The ability is a reference to Thou Shalt Not Die (君死給勿, Kimi Shinitamō Koto Nakare?), a poem by Akiko Yosano in 1904. It is a poem addressed to her younger brother who has been sent to fight in the Russo-Japanese War, telling him not to die. It was also made into a song and was used as a mild form of anti-war protest.
- When Atsushi Nakajima saw and worried about Doppo Kunikida's amputation, the latter hinted that Yosano can do something about his condition. Though it is yet to be expounded upon, it hints on the potential of Yosano's ability to allow regeneration or restoration.