The following contains spoilers for The Last of Us Season 1, Episode 6, "Kin" and Episode 7, "Left Behind," now streaming on HBO and HBO Max.

The Last of Us Season 1, Episode 7, "Left Behind," is essential viewing, according to star Storm Reid.

Reid, who portrays Riley Abel, outlined what makes the seventh episode so crucial to the HBO series' overarching narrative in an interview with Vulture. "It brings more complexity to the show," she said. "The episodes that we've seen thus far, we've seen perspectives of the older characters. To now see Ellie's perspective from before she met Joel, you get to see how she moves through the world, how she takes up space. It gives audiences a little bit more backstory of who Ellie is. It's a fresh perspective."

Related: The Last of Us: How Ellie Got her Eyebrow Scar

The focus on Ellie's history in "Left Behind" comes after The Last of Us hinted at her future in Episode 6, "Kin." That episode includes a conversation between Ellie (Bella Ramsey) and Joel (Pedro Pascal) about her favorite astronaut, which was inspired by the original video game's sequel, The Last of Us Part II. According to showrunner Craig Mazin, this nod to the second Last of Us game was added to the "Kin" script as a way of illustrating how far Ellie and Joel's relationship had progressed.

The Last of Us Star Talks Joel and Tommy

The Last of Us' sixth episode also spotlights the dynamic between Joel and his brother Tommy (Gabriel Luna). Luna recently spoke about how he and Pascal communicated a sibling bond between them in their scenes together by drawing on their similar experiences growing up. "[Pascal] was born in Chile, but he was raised in San Antonio, Texas," Luna said. "So right there off the bat we had that in common with our characters, we had that in common with each other."

Related: HBO's The Last of Us Finally Expands on Ellie and Riley's Past

Luna mentioned the other influences on his portrayal of Tommy in The Last of Us in a previous interview, which included his work on several other high-profile franchises. "It ended up being a matter of refreshing many of the skills that I've acquired. All the combat training I've ever done -- and whether it be for Matador, for the Ghost Rider [in Agents of S.H.I.E.L.D.], for Terminator or any of those things," he said. Luna added that he also brushed up on his horse-riding skills prior to filming, recalling that this was an important gameplay mechanic in the original game.

New episodes of HBO's The Last of Us air every Sunday.

Source: Vulture