Attack On Titan Vol. 4 by Isayama Hajime

Eren has finally reclaimed his senses in titan form and picked up the bigass rock he was assigned to carry. This rock will plug up the hole in the wall that has been allowing titans to enter unimpeded. If completed successfully, this mission will serve as the very first time in human history that people have taken any of their land back from the titans. With the rock finally in its proper place it's a historic moment as well as a historic mission, but there's a heavy cost to it all. 

After the wall is plugged up and Armin, Mikasa, and a now exhausted human-sized Eren have been rescued by Captain Levi, we are transported into the past just a bit and it is there that we spend the bulk of this issue. 

I rather like the flashbacks in Attack on Titan because these flashbacks are always things we haven't seen before and they really do add an extra layer to the story. It's one thing to see Eren, Mikasa, and Armin fighting titans, but it's another to see how Eren's determination actually got him through boot camp. It's these little touches that sort of break the intense doom and gloom of the series every now and then. 

These flashbacks also let us see the "potato girl incident" hilariously depicted in the anime. Honestly, I wasn't sure if the flashbacks were filler or not as I began reading the manga because the flashbacks seemed to take place a bit earlier in the anime. So discovering that those segments were actually canon was a relief. This issue is divided into episodes 3 and 13 in the anime (as best as I can recall anyway), which essentially means that this issue brings us halfway through the show since 13.5 was a recap episode. 

Once the flashback is concluded Eren wakes up in a cell and meets Captain Levi and Commander Erwin of the Survey Corps. After Eren makes it known how badly he wants to kill the titans Levi and Erwin agree that he would fit in well with the Survey Corps. There's a catch, though. If Eren loses control of his titan powers Levi will kill him. And if you are unfamiliar with Levi then you should know that Levi is probably one of the few who really could.