Warning: Spoilers for Trigun Stampede, Episode 8After revealing Vash's status as a plant at the end of the last episode, Trigun Stampede takes a step into the past to look at Vash's background since the crash, and it's taken some wild turns away from both the original manga and anime.
The entirety of episode 8 revolves around a young Vash escaping the wreckage of Ship Five of the SEEDS fleet, which Knives had brought crashing down onto the planet. Vash is found as one of the few survivors by those aboard a ship that managed to survive, and while they mistrust him initially, they take him in, and he lives with them for years. When his connection to Knives is found in Trigun Stampede, and they learn that Knives didn't die, Vash runs off and nearly dies. He awakens back aboard the ship with a new arm and discovers that Knives has once again killed everyone close to him.
Vash's Various Backstories
For anyone familiar with previous iterations of Trigun, there's quite a bit here which seems to be entirely new. In the manga, Vash doesn't know what to do after the ship crashes, and he ends up following Knives around for over a decade. Knives gives Vash his signature gun during this time, and the two separate when Vash accidentally shoots Knives. In the 1998 anime, Vash and Knives similarly travel together for a long time, but when Knives admits to his plan to kill the humans to save the Plants, Vash considers killing him briefly. He receives the gun again in the same way, but then Vash shoots Knives deliberately in an argument before fleeing. After that, he stays with some survivors from the fleet for a while aboard a functioning ship in space where he receives his red coat, before returning to the ground.
The new backstory clearly borrows from both previous series, but it also diverges in a major way. Here, Vash flees from Knives as soon as the ship crashes, and the two don't see each other for years. Vash spends time with the survivors and gets to know them, and they are largely original characters not present in the other versions. He is able to earn their trust by communicating with the Plants for them, establishing the ability he was seen using at the end of the previous episode. It also establishes the pattern that would come to dominate Vash's life: he meets people, gets to know and like them, and they're then killed by Knives for the crime of associating with Vash. While the guns have not factored into the backstory yet (they appear to be in the next episode), the red coat did appear as a gift given by the ship's captain.
This reshuffling of Vash's backstory may have something to do with Trigun Stampede's seemingly earlier setting chronologically; if Meryl has run into Vash at a younger point in their lives, then there are certain backstory events that may not yet have taken place. The end of Trigun Stampede's first season seems to be setting up for an epic confrontation between the two, and with just a few episodes left, it'll all come to a head soon enough.
Trigun Stampede debuts new episodes on Saturdays, via Crunchyroll.