Soulkiller

Soulkiller is a Black Program written by Alt Cunningham, later stolen by Arasaka.

Background
Developed in a lab on the 120th floor of Arasaka Towers in 2013, the Soulkiller virus is a program capable of creating a digital emulation or copy of a netrunner's mind, utilizing an advanced matrix recorder storing it in a huge database. It then wipes the original personality away, leaving a mindless husk that eventually dies. Few mainframes in the world are capable of running the program, with the only mainframes running it present in Arasaka Towers in Night City, or in Tokyo.

2013
In 2013, Alt Cunningham was abducted by Arasaka and experimented on by Toshiro to test the Soulkiller software. Johnny Silverhand mistakenly disconnected Alt from the Netrunner chain, believing she was undergoing a test of some sort. This caused the link between Alt's engram and body to disconnect, effectively killing physical embodiment in the process and leaving her stranded in the net.

2023
In 2023, shortly after the nuclear bombing of Arasaka Tower, Saburo Arasaka ordered the Soukiller to be used on Johnny Silverhand, who had been captured and evacuated from Night City before the bomb detonated. Silverhand's mind was later transferred to the Relic.

2077
In 2077, after multiple Relic 1.0 failures, Hellman decided to try out the 2.0 experimental version due to pressure from Yorinobu Arasaka and his investors. With a long list of VIP engrams ready to be used due to Soulkiller being used in secret, Hellman decided to put Johnny Silverhand's engram on the new version of the Relic due to belief that the experimental version would fail and would destroy an undesirable engram like Johnny Silverhand in the process.

Alt Cunningham appears after V breaches the blackwall to ask about the Soulkiller program. It is revealed that she is not Alt Cunningham but an image of her due to Johnny Silverhand severing the connection between her engram and body which hosted her consciousness while trying to rescue her. For 50 years she held onto the image of Alt to ensure she did not get turned into complete data like other AIs.

Path of Glory/Assault on Arasaka - Ending
It is later revealed by the AI version of Alt Cunningham that the Soulkiller only copies the psyche and memories of a person, effectively killing the person in the process and does not transfer a consciousness to the engram or net. But if the host is still connected to the Soulkiller the engram can be transferred back to the host's body and overwrite any previous engram's on it, giving V a chance to overwrite Johnny Silverhand's psyche and memories from their brain while keeping their consciousness and memories, as Hellman was planning on leaving Arasaka.

Johnny Silverhand's engram later admits that he has always been dead due to the Soulkiller actually killing souls and believes his nature is to rebel from beyond the grave to honor the real Johnny Silverhand's mission. After this realization, Johnny Silverhand decides to save V's consciousness and memories by leaving the Relic and following Alt Cunningham beyond the Blackwall and to fuse with her mind as raw data along with other engrams that are trapped in Mikoshi.

Despite V successfully removing Johnny's engram, they're always given 6 months to live regardless of ending due to the neural damage that the Relic caused them.

The Devil - Ending
Arasaka successfully commercializes the Relic program after Hellman reports to Hanako Arasaka the results of V and Johnny Silverhand's Relic malfunction. The first subject for this program becomes Yorinobu who had failed a hostile takeover of Arasaka and was on the verge of killing himself before V intervened. To restore his honor he agrees with Hanako that he will let his father take over his body and mind, who had his body secretly subjected to the Soulkiller program after his death. While Alt is not present to clarify the repercussions of being Soulkilled, several characters, including V, will point out that engrams from the dead are not really human consciousnesses but simply data masquerading as them.

Unfortunately Arasaka fails to save V's mind from deteriorating after surgically removing the Relic from their head. According to Arasaka, Johnny's imprint is wiped and destroyed but that doesn't stop him from visiting him in his dreams. Due to V's mind deteriorating and Arasaka being unable to help, they have the option to save their engram with Soulkiller and have it transferred to Mikoshi until they can find a suitable body, if ever. This essentially means V chooses death while their data can be stored somewhere for the far future, according to Hellman or Takemura.