Warning: Contains SPOILERS for The Last of Us season 2, episode 6!
The Last of Us season 2, episode 2 killed off Joel, sending Ellie off on her quest for revenge without one of season 1's main protagonists. However, the trailers for The Last of Us season 2 clearly showed new footage of Joel, meaning that many fans expected flashback sequences to come. The Last of Us Part II is full of flashbacks of Joel and Ellie, and while scenes like Joel and Ellie's museum trip are ripped straight from the game, episode 6 of The Last of Us season 2 also features some original scenes.
"Future Days" Was The First Song Joel Performed For Ellie In The Last Of Us
After He Gifted Her The Guitar
While there are a few exceptions, most of the flashbacks in The Last of Us season 2, episode 6 take place on Ellie's various birthdays between seasons 1 and 2. One of these scenes sees Joel gift Ellie a guitar, kicking off the love for music that she has shown in The Last of Us season 2. After she receives the guitar, she asks Joel to perform a song for her. Joel decides to play and sing the Pearl Jam song "Future Days," with Ellie listening as he performs the emotional song.
The use of Pearl Jam's "Future Days" comes from The Last of Us Part II, although it does require an interesting retcon. HBO's The Last of Us uses a different timeline than the video game, with the outbreak occurring in 2003 in the HBO series and in 2013 in the source material. Pearl Jam's "Future Days" was released in 2013, so while it makes sense for Joel and Ellie to know the song in the game's timeline, it shouldn't exist in the HBO series.
The Last Of Us Season 2's Guitar Flashback Explains Why Ellie Couldn't Play "Future Days" In Seattle
It Was Too Painful For Her
Now that we have been provided context for why "Future Days" is significant, Ellie's performance of the song in episode 5 makes a lot more sense. Joel performing the song when Ellie got her guitar is probably a key memory for her. It would be hard for her to not think of Joel when hearing the song or even when playing guitar. Thus, it was probably too painful for her to sing "Future Days," explaining why she quit so quickly.
Joel's performance of "Future Days" also adds an interesting subtext to Ellie's revenge story. Ellie's choice to perform the song highlights how Joel's death has taken over every aspect of her life. She can't even do things she enjoys, like play guitar, without thinking about him. This motivates Ellie's quest for revenge even further, highlighting how obsessed she is with finding Abby. This theme will probably be explored further in future episodes of The Last of Us, making this one of the show's most significant flashbacks.