The Beating of a Heart Can Be Heard

I Can Hear His Kokoro Going Dokidoki is the fifth chapter in the second volume and the ninth chapter overall of the manga Shingeki no Kyojin.

Summary
The rogue titan is still fighting the titans outside and seems to be making short work of them. Sceptical, Reiner questions Conny about how much he actually knows about the rogue titan. Conny replies that he doesn't care, as it saved their lives.

With seven 3-4 meter class titans in the supply room, they still aren't able to restock. Looking for anything that might help, the group finds some old guns in the headquarters. While some question their usefulness, Armin is able to form a strategy. Using the lift, one group, armed with the guns, will be lowered down into the room to get the titans attention. When the titans move in, they will fire into their eyes, temporarily blinding them. A second group, waiting above, will then jump down and go straight for their weak spot. The significant amount of risk, causes Armin to second guess himself; however, it's their only option. Mikasa comforts Armin, saying that his ability to strategize has saved both her and Eren in the past. He starts to ask when, but is cut short on getting an answer when the lift is prepared. The second group goes over their part and gets into position. Group one proceeds down the lift, quickly gaining the titans attention. Nervous, they anxiously wait until the titans are close enough. Nearly on top of them, group one fires their weapons into the faces of the giants. Group two then jumps down with everyone but Sasha and Conny killing their target. The others rush in to back them up with Mikasa saving Sasha and Annie saving Conny.

The room now clear and no more coming in, they move in to restock their dwindling supplies. As soon as their tanks are full, the group moves out except for Mikasa. Armin goes to see what's wrong. She notices the rogue titan getting attacking and eaten by others and regrets that they couldn't learn more. Reiner, Jean, Annie and Berthold join them on the roof. Hearing the conversation, Reiner agrees with Mikasa and suggests helping it out. Jean isn't sure he's ready to risk his life for a titan, especially since they just barely survived their last encounter. Annie also agrees with Mikasa, especially with the possibility of having a titan as an ally. Out of nowhere, Armin catches sight of the titan that killed Tomas. Suddenly, the rogue titan bursts away from his attackers, lunging for that same titan and bites through the back of its neck. In one motion, he slings the body in his mouth into another titan, sending them both crashing through a building. With that, he collapses, seemingly exhausted. Jean, again questions if it can become an ally, saying a titan remains a titan. Without warning, smoke starts to rise from the back of the rogue titans neck. Out of the smoke they see the body of Eren Yeager. Mikasa is the first to rush down, followed by Armin. Miraculously, he's alive and what's more, the arm and leg that were missing have completely regenerated. The others, surveying the dead titans now see that it was the work of Eren and wonder if they do in fact have a titan for an ally.