Lance Corporal Rivaille is a special chapter at the beginning of the third volume.
Summary
We are taken back to the beginning of the history of the Titans and given a brief synopsis of the events so far. One hundred years ago, titans appeared and threatened to wipe out all of mankind. Somehow, the humans were able to build a giant three layer, walled city and managed to live in peace for the next hundred years. However, five years ago, the appearance of the Colossal Titan changed all that. With the outermost wall destroyed, twenty percent of the population was wiped out in only three minutes, causing the remainder to retreat to th esafety of the second wall. It was at this time that Eren Jaeger vowed to kill them all, due to the death of his mother.
Five years later, we are introduced to Commander Rivaille, humanities strongest soldier, said to have the equivalent combat force of an entire brigade. As he and others in the Scouting Legion parade through the street on their way to the gates, Eren, Mikasa and Armin stare at him in amazement. A teammate, jokes that they would be heartbroken if they knew how much of a clean freak he was.
Each time the Scouting Legion went out, they would typically lose thirty percent of their forces, which is what made soldiers like Rivaille so important. While out on a mission, one of his comrades is caught by a titan. Half inside the giants mouth, he threatens him, saying that humans will overthrow them, particularly Commander Rivaille. As he says this, Rivaille shows up and attacks the titan, killing it. With reinforcements arriving, he orders Petra to take care of the wounded. He then orders the reinforcements to take the right flank, while he takes the left. Making short work of a group of titans, he thinks to himself that they are all the same; the same ridiculous faces. He gets blood on his hands when he finishes a titan off, causing him to take pause and immediately clean it up. Taking a short break, he joins Petra and the soldier he saved earlier. With the soldiers dying breath, he asks Rivaille if he has been useful. Encouraging him, he takes the soldiers hand and tells him he has done more than enough, which allows him to die in peace. A soldier approaches them on a horse, informing them that they must retreat. When Rivaille questions why, the soldier informs him of the latest attack on the city and the movement of the titans toward it. Worried that the wall may already be broken, they leave.