- "Trying hard to keep track of how long I have been here. Strange, fractured land."
- — Kazimir Zykov
Kazimir Zykov was a sergeant and mechanic of the 1st Guards Tank Army who scavenged parts from German Panzer tanks to repair Soviet T-34s. In 1945, he was met by Colonel Pavel Lazarev, who tasked him with shutting down the Projekt Endstation cyclotron. Zykov accepted the task, and was soon sealed within the facility all alone, fending off against the undead while desperately finding a way to disable the cyclotron. Eventually, Zykov succeeded in his mission by closing the breach from within the Dark Aether, though this would ultimately leave him trapped with no means of escape.
His first year was marked by the exploration of the Dark Aether which he described as a "strange, fractured land". He started gathering food and water as well as electronics in hope to build a transmitter. He noted that, in addition to the undead, other people were also trapped in this dimension, but always tried to avoid them. At one point, Zykov encountered a group of people sheltered in a warehouse. He tried to save the group as Plaguehounds were approaching. Zykov managed to pull at least one person out of the warehouse, but he ran back inside while the hounds were still there. The first year ended with a complete base of operations with stockpiled weapons, a "little fort". The base featured barricades and traps in case the creatures from the Dark Aether came too close.
During the second year, Zykov gathered lots of electronics but was unsuccessful in building the transmitter. He, however, found "weak spots" where the Dark Aether overlap with their original world. While he couldn't pass through, he caught a glimpse of Southeast Asia.
In the third year, Zykov made several attempts to pass through the weak spots and managed to enter his world for a brief period of time, usually 10 or 15 seconds before being pulled back in the Dark Aether. He visited different locations each time including a village, a jungle and a glacier. Zykov noted that while in their world he wandered unseen, "like a ghost".
The fourth year was marked by his encounter with an Elder God, as some of the survivors called them. Zykov described them as "tall as building". He kept their distance as the creature passed.
During the seventh year, Zykov managed to visit his world for almost 30 seconds. He arrived in a military base where soldiers communicated on a equipment similar to the electronics they gathered. Knowing how it was meant to operate, Zykov returned to his transmitter project. By this point, he was now eating the creatures living in the Dark Aether to survive, noting that consumption of the vegetation yielded in "poor results".
In the eighth year, Zykov managed to visit his world for several minutes. He believed to have arrived in New York City observing "tall glass buildings" and "long cars with fins on tails". Nobody noticed him and the world went without him. Zykov noticed during that year that fewer creatures were pursuing them while still attacking newcomers. However, the powerful creatures have started to notice his presence.
During his tenth year in the Dark Aether, Zykov managed to tame an injured Hellhound and nursed him back to health. The hound was now answering his calls, and stayed close and hunted alongside him. Zykov gave him the name "Cinder" and gave him a place within his fort, keeping it warm. He wished, however, he could pet the hound.
During the eleventh year, he found a dead Elder God, also referred to as an Overlord, with talk that one of them was hunting the rest. Zykov first thought it was crazy talk as some survivors were worshipping those giants, though he soon started to believe the rumors and worried about what could happen if one of the Elder God imposed its will on the others.
In the sixteenth year, he found several "machines filled with beverages". Believing them to be a trap, he let other survivors consume what the machines had to offer. He then realized that the beverages had "profound effects useful for combat". He noted that the machines also played music while dispensing the beverages. At one point, he found a red beverage machine which was badly damaged with the internals exposed. He tried to fix it but some parts were beyond repair.
During the seventeenth, Zykov found a new broken device looking like a a kiln, or a crucible but couldn't fix it. He started considering looking for help. He also became confident that they could complete the transmitter project. Zykov encountered another survivor who was trading items and components and told them about the machines they were repairing. Four days later, however, the Trader arrived with several survivors to attack Zykov's fort. He avoided the trap and broke in. Cinder attacked the invaders but was killed while Zykov was almost burned alive when his only friend exploded. The group stole all the machines and components before leaving the fort. Two days later, Zykov visited the Trader to make peace at first, as human life is rare and precious in the Dark Aether. When they refused his offer, Zykov killed them all. He noted that while they knew that there was still good in humanity, the longer he was in the Dark Aether, the less he remembered what it was.
Twenty years later, 37 years after becoming stuck in the Dark Aether, Zykov finished his transmitter and started broadcasting his journal of survival, hoping someone was listening. Ten days later, he found a device set to the frequency he was using for broadcasts in a weak spot. He could see all his transmissions on the screen. After being pulled back, he set his transmitter to indicate if the receiving device has been used, and began looking forward to any sign of someone on the other end.
During Requiem's undertaking of Operation Threshold, Zykov resumed contact through the device, informing those on the other side that he would be working on a way to create vocal transmissions, as well as stating their intent to inform them about the going-ons of the Dark Aether, stating that Requiem's lives "may depend on it". Sometime later, Zykov succeeded in making vocal contact, informing those on the other end that he was Russian, and that he had encountered both electric men that float mid-air and armored monsters. After continuing to observe their fighting, Zykov decides to reveal his true identity to Requiem.