Where we last left off, Levi fires a noise grenade to remind his squad of their current objective. Meanwhile, the Female Titan is still chasing Squad Levi, killing anything that tries to stop her. Eren doesn’t seem to understand why they’re just leaving them to die and tries to Titan-shift. However, before he does, Levi offers him a choice: To trust in his own abilities or to believe in the Survey Corps’.
Anyway, we get a flashback, which probably would’ve made more sense if it was in a previous episode before the arc began. It involves the Survey Corps putting Eren in a well and hold him there so he can control himself in Titan form.
As you know, Eren shifts into Titan form via self-inflicted injury. So he does that by biting on his thumb. However, for some reason, Eren finds out that he can’t transform. His bite wounds on this thumbs don’t seem to be healing, either. Oddly enough, when he tries to pick up a spoon he dropped, a portion of a Titan body manifests.
After a moment where everyone begins SHOUTING AT RANDOM, Hanji deduces, while her eyewear mysteriously changes from goggles to glasses then back to goggles, that Eren is only able to Titan-shift not only through self-inflicted injury, but when he has a clear objective in his mind. Like “Kill the Titans” or “Block the cannon shell” or “Lift the boulder,” which, if you ask me, is a rather bullshit reason to limit his powers.
Anyway, flashback over, Eren decides to move forward. Of course, later do we realize that they were only luring her into a trap to capture her alive and cut her open to find out who is the face behind the Titan…
So yeah, kinda lackluster here. Again, BS reason for Eren’s Titan-shifting powers.