Here's how Black Mirror season 5, episode 1, "Striking Vipers", fits into the Netflix show's shared universe. While Black Mirror is an anthology show, there are enough Easter eggs and recurring themes to place them on a timeline. "Striking Vipers" has the most connections to season 3's "Playtest", although the final narrative outcomes are much different for the main players involved.
Black Mirror season 3's "Playtest" focuses on a test gone wrong. The episode follows an American traveler in England (Cooper, played by Wyatt Russell) who needs money, and volunteers to be a research subject for a famous video game developer. He’s briefly (and knowingly) immersed into a horror-themed virtual reality, but dies when an incoming cell phone signal disrupts a VR upload sequence. In Black Mirror season 5, "Striking Vipers" features two adult male friends (Anthony Mackie's Danny and Yahya Abdul-Mateen II's Karl) who begin a sexual relationship within a virtual reality video game as different people. In real life, they discover there’s no physical attraction, but the pals continue to have monthly VR sex, with the approval of Danny's wife.
Not only do both these Black Mirror episodes see characters embrace new technology for practical reasons, they're doing so with the same tech. In "Playtest", Cooper spots an online job opportunity and seeks out famous video game developer Shou Saito, the founder of SaitoGemu. In “Striking Vipers,” the Striking Vipers X (Immersive VR Edition) game that reunites by Danny and Karl is published by SaitoGemu, as evidenced by their logo on the box.
These are the primary references to SaitoGemu in Black Mirror, but certainly not the only ones. The company was also referenced in a news ticker during the Black Mirror season 3 episode "Hated in the Nation", and in both season 5 episodes, "Smithereens" and "Rachel, Jack and Ashley Too" by hashtags and news ticker respectively. It would appear that "Striking Vipers" occurs later in the timeline than the majority, after the technology is popularized.
The world-building doesn't end there, however. The VR add-on that enables the game is made by TCKR System, the company responsible for creating the virtual reality in "San Junipero," and where Rolo Haynes from "Black Museum" previously worked. This deepens the world but also further explains the connections between the two primary episodes. In "Playtest," the SaitoGemu virtual reality technology uses a “mushroom" inserted into the back of the neck, which appears to be quite similar to the "disc doohickey" used in "Striking Vipers." In the season 5 episode, it appears that SaitoGemu’s mushroom technology is now part of TCKR's VR add-on, allowing Karl and Danny to instantaneously transport into a virtual reality existence.
It's not just the world of Black Mirror that connects "Playtest" and "Striking Vipers." The concepts of time and personal development are crucial to both episodes. Cooper doesn’t quite understand what will happen at SaitoGemu, or what he’s supposed to see. In contrast, Danny and Karl schedule their first VR meeting in "Striking Vipers" without understanding how they’ll react to each other, or how long they might stay within the video game world. Both episodes feature safe words (“Stop,” “Exit Game”), yet neither work: Cooper’s SaitoGemu VR experience ends just as it begins (0.04 seconds), whereas “Striking Vipers” ends with Danny and Karl scheduling VR sex sessions once a month on a Friday night. Thanks to Cooper's failed experiment in "Playtest," Danny and Karl are able to better understand themselves as people. They learn how to live.