Mercy

The moment Annie's identity is exposed, Armin sends up a flare and hidden soldiers pile onto her. Their grip is not enough. A concealed spike flicks out of her ring, she cuts her thumb, and the resulting transformation rips her captors apart. Mikasa spots the ring just in time to drag Eren and Armin down the stairway before the blast.

Underground, the three press deeper as a massive arm claws after them. Armin wavers, second-guessing his own scheme, until Mikasa forces him back to the problem at hand. They move to trigger the backup plan, but the Female Titan stomps straight through the street above, crushing the waiting squad and caving in the passage. Armin reads the recklessness of that strike for what it is: desperation to seize Eren at any cost. Now they are pinned, visible through the new hole if they advance, crushable if they stay.

Eren bites his hand to shift and protect them. Nothing happens. He tries again while Armin urges him to fix his purpose in mind, and still his body refuses. Mikasa wonders aloud whether he doubts, deep down, that the girl above them is really Annie.

A flashback lays out how the operation came together. Days after the failed expedition, Erwin briefs Eren and Levi: the Female Titan has been identified and will be lured using Eren as bait. Armin built the case. Annie knew Eren's face and searched faces as she killed; she reacted to the nickname Suicidal Blockhead, known only to their training class; and when equipment was inspected after the captive Titans were destroyed, she presented Marco's gear rather than her own. Mikasa adds the simplest tell, the resemblance between Annie and the Titan itself. Eren resists accusing a friend but eventually gives in, remembering how her signature kick once finished their sparring match.

In the present, Armin proposes the only exit left: he and Mikasa burst out through opposite ends of the tunnel, splitting Annie's attention and giving the others a chance. Eren protests, and Mikasa answers that the world is cruel, so what choice remains. Watching his friends risk themselves crystallizes something in him. He bites down, erupts through the street in Titan form, and opens the duel with an uppercut that launches Annie off her feet.

Mercy runs within The Female Titan arc, following Grin and preceding Wall. Japan saw it on April 9, 2012, with Kodansha's English release arriving October 29, 2013. The anime spread its events across the two Stohess episodes, Smile and Mercy.

An art inconsistency slips through the chapter: before transforming, Annie's uniform repeatedly carries the Survey Corps emblem even though she serves in the Military Police Brigade.

The chapter quote is Mikasa's blunt reminder to Eren that Annie and the Female Titan are one and the same, the doubt she suspects is blocking his transformation.