WARNING: The following contains spoilers for Season 4, Episode 9 of Attack on Titan, "Brave Volunteers," streaming now on Crunchyroll, Funimation, Amazon Prime and Hulu.
Episode 9 of Attack on Titan not only flashes back three years prior to Season 4's start -- the surprise reappearance of an old adversary harks all the way back to the anime's very first season. This cameo is Annie Leonhart, holder of the Female Titan and once Eren's toughest opponent in his early days wielding the Attack Titan.
But Annie's reemergence in the series isn't a simple reminder of the Marleyan Warrior's existence, trapped behind enemy lines in a crystal shell. The scene has as much to do with the person keeping her immobilized body company that it does with her, as well as what the content of their one-sided conversation reveals about Eren's strained relationship with one of his oldest friends.
It's no secret by now that Eren and the Survey Corps are feuding with one another. The raid on Liberio in Marley appears to have been entirely his idea, with the Scouts merely tagged-in to act as back-up rather than leading the charge with him. From Mikasa to Armin to Jean to Levi, the discontent has been stewing barely below the surface for several episodes (or not at all in Levi's face-kicking case). Even with Paradis Island's finest scoring their biggest victory to date over Marley -- reclaiming both the War Hammer and Beast Titans and utterly squashing the Jaw and Cart Titans -- Eren remains both physically and emotionally distant from his allies upon their return home.
This couldn't be better encapsulated than in Armin's decision to vent at someone so far removed from the situation, she can't even answer back. It's not even clear whether Annie's conscious or not at this stage, though the War Hammer Titan's previous use of this tactic indicates it's certainly possible. After being defeated in Season 1, Annie, much like the late Lara Tybur, crystallized herself to ensure her survival on the Island, stop herself from being tortured into giving away Marley's secrets or have her power stolen. She's been kept underground by the Eldian military ever since and, evidently, Armin has made a habit of visiting her.
In Episode 9 of Season 4, Armin bemoans the fact that he doesn't know Eren as well as he used to, fearing what he might do next. Now that Paradis has secured both the Founding Titan and a person of royal blood (Zeke) that they're willing to sacrifice, activating the Rumbling is closer to being a real possibility. Flashback scenes also confirm Eren is far from opposed to ruling out this devastating event as a way to secure Paradis' future.
It's interesting, too, that while Armin ponders all this in front of Annie in the present-day, he has the seashell in his hand from the beach the Scouts reached at the climax of Season 3. That day, like many others in the series' history, was a historic one. The day Eren pointed across the ocean at their "true" enemy -- Marley. Armin obviously recognizes that this was a turning point in his childhood friends' outlook. Annie, too, is a relic of a simpler past, comparatively, when the line between good and evil was clearer and the rest of the world was an unknown line on a horizon the Islanders could never reach.
But that isn't to say Annie's reintroduction into Attack on Titan is a purely symbolic one. As we were reminded of by Eren's baseball mitt in Episode 4, nothing in the series is incidental. It's only inevitable now that Annie won't stay frozen for much longer. The question is, once free again, whose side will she choose in this new war?