The following contains spoilers for The Last of Us Season 1, Episode 9, "Look for the Light," which debuted Sunday, March 12 on HBO.
HBOs The Last of Us significantly expanded Ellie's backstory from the video games. Season 1 included the adventure from the Left Behind DLC that revealed how Ellie learned she was immune, as well as time growing up in a FEDRA school as an orphan. The finale "Look for the Light" goes even deeper into her backstory by traveling back to show the day of her birth and introduce Ellie's mother Anna. The tragic story is gut-wrenching, but explains so much about Ellie.
That same flashback also solidifies the connection between the Fireflies' leader Marlene and Ellie that had been left vague all season. Prior to the finale, it had been mentioned that Marlene dropped Ellie off with FEDRA when she was an infant and that when Ellie grew up, Marlene denied her entry to the Fireflies. The Last of Us finale details Marlene's motivations for those decisions when it unravels the complicated relationship between these two characters.
What Was Marlene's Relationship to Ellie's Mom?
When Ellie was being tested for immunity by the Fireflies, there was a hint about her history with Marlene. The leader of the Fireflies was the person who left the orphaned Ellie to be raised by FEDRA. The Last of Us finale reveals the connection between the two: Ellie's mother Anna was also Marlene's lifelong best friend. But while the flashback shows Anna had obvious maternal instincts, Marlene's personality isn't particularly maternal, nor are her priorities.
Marlene clearly feels guilty that she wasn't there to support her best friend through her childbirth, but doesn't appear to have any personal interest in pursuing motherhood herself. Anna seems to recognize this and so she doesn't ask Marlene to personally raise and protect Ellie; she just requests that Marlene place Ellie somewhere safe. It's a specific distinction that speaks to how deeply the two women understand each other. When Anna begins to turn as a result of her infection, she asks Marlene to kill her as a final act of mercy. Initally Marlene denies her request, but ultimately she acquiesces to her best friend... just as Ellie later kills her friend Riley.
Why Marlene Didn't Let Ellie Join the Fireflies
Marlene admits to Ellie that she dropped her off with FEDRA despite the Fireflies and FEDRA being on opposite sides of a war. The Last of Us finale explains that this was Marlene's way of honoring her best friend's final wish. Ellie would be raised in an environment designed to keep children alive, if not entirely happy. The Fireflies were not a safe community in which to raise a child. They were constantly on the run and had to survive incredible hardships while being pursued by FEDRA. They also deliberately enacted violence as a form of rebellion. Marlene could not be responsbile for Ellie -- which is why she wasn't raised as a Firefly.
It was likely too emotionally painful for Marlene to try and find a way to connect with Ellie. It would have required Marlene to confront her feelings about Anna's death, which could have been distracting from her larger cause. And welcoming Ellie into the Fireflies would definitely have been a liability. Both Joel and Tess (however briefly) became attached to Ellie. There's something about Ellie that draws people in, but Marlene couldn't allow herself that luxury of an emotional connection. Her priorities will always be what's best for the Fireflies, and allowing Ellie to join the Fireflies would have also been contrary to Anna's last wish to keep Ellie safe. The Last of Us finally provides context for the decisions Marlene made -- just before her heartbreaking death.
The Last of Us Season 1 is now streaming on HBO Max.