To obtain, something of equal value must be lost. That is Alchemy’s First Law of Equivalent Exchange.
—Alphonse Elric from Hiromu Arakawa’s Fullmetal Alchemist
In the early Babylon 5 episode “Deathwalker,” the war criminal Jha’dur appeared on the station with an anti-aging drug. Despite calls for her trial and execution by her victims, the member species of the League of Non-Aligned Worlds, Cmdr. Jeffrey Sinclair and Jha’dur convinced the assembled powers to let her go, albeit temporarily, in return for mass-production of the drug and the promise of eternal youth. However, as she prepared to leave the station, Jha’dur revealed to Sinclair that the immortality drug couldn’t be manufactured without components taken from living people through a process that will kill the donors. That is, for one person to gain immortality others must die.
The alien energy transfer device, first introduced in “The Quality of Mercy,” was originally used to punish criminals through the transfer of their life force to another person. The more injured the recipient, the more life force was required to heal them. In extreme cases, the device could completely heal a dying patient at the cost of the donor’s life. The device played a critical role in the series on two occasions. The device was used by Dr. Stephen Franklin and Capt. John Sheridan to revive Chief Michael Garibaldi, after he was critically injured in a failed attempt to prevent the assassination of President Santiago (“Revelations”). The device was last and most memorably used by Marcus Cole to save the life of Cmdr. Susan Ivanova, albeit at the cost of his life (“Endgame”).