First Battle

Their First Battle, is the fourth chapter of Shingeki no Kyojin.

Summary
The Colossal Titan, who hasn't been seen in five years, appears out of nowhere and Eren and his companions are attempting to counter his attack on the wall.

Using his Three Dimensional Maneuver Gear, Eren climbs the Colossal Titans arm and goes for its head. Along the way, he notices that the titan isn't attacking at random, it's taking out cannons and aiming for vital spots on the wall. Going in for the kill, Eren heads for the weak spot on the back of the neck. However, the Colossal Titan emits a burning gas and temporarily disorients Eren. When the smoke clears, the titan is gone leaving Eren confused.

Soon after, a member of the Stationary Troops shows up and tells the trainees that the Colossal Titan strategy has started. He then orders Eren to report to headquarters due to making contact with the titan. With the Scouting Legion out on exploration, the Stationary Troops are the only military presence available to repair the wall and prepare for an ambush. The city is once again in a panic. The lack of soldiers puts the trainees in the sink or swim position of filling in the gaps.

Eren finds Armin, who quickly give him a run down of the dire situation. There is an eight meter high hole in the wall and the rock meant to fill it in hasn't even been excavated yet. With the hole there, the city will be abandoned and Wall Rose will be vulnerable. Briefly letting the fear get the better of him, Armin worries that the titans could eradicate humanity at any time. Eren calms him and he is able to gather himself and continue his work.

The trainees are given their instructions. They will be divided into three groups, the front, middle and rear guard. The trainees are made aware of their commitment; fleeing in front of the enemy will be met with capital punishment and they are to give their live if necessary. As they are dismissed, Mikasa tells Eren to find her if things get confused in battle. However, she is then assigned to the rear guard due to her superior physical abilities, making the request to Eren difficult. Angry, Eren tells Mikasa to stop trying to impose her own rules; he then apologizes for getting carried away. Distraught, Mikasa has one more request for Eren...don't get killed.

Eren thinks back to how little is known about the titans. The information they do have is all thanks to the Scouting Legion. What they do know, is that the titans don't show interest in eating any creature other than humans and they've lived largely devoid of humas for 100 years; which suggests it isn't for nourishment. What stands out even more, is their vitality and ability to heal from seemingly devastating wounds. The only spot they can't regenerate from is at the nape of the neck; a blow which is best delivered using Three Dimensional Maneuver Gear.

Now on top of a roof in their assigned position, Eren and Armin, along with other trainees, prepare for the task ahead. Eren, encouraging Armin, says that they should be able to rise through the ranks of the Scouting Legion quickly if they start practicing now. Not wanting to be outdone like the previous encounter, Tomas and other trainees suggest a titan hunting contest and with that, they are on their way. Almost immediately, they run into titans who have come through the hole in the wall. It seems that the front guard already have more than they can handle. As the group is moving along the rooftops, a titan lunges for an attack. They scatter but unfortunately, Tomas isn't fast enough and gets caught. Eren watches in terror as his teammate gets swallowed whole. Now in a rage, he rushes off to try and kill a titan with its back turned; not noticing the titan that is below him. The titan jumps up and bites off Eren's leg below the knee. Watching Eren bleeding and stranded on a nearby rooftop, Armin goes blank. The remainder of the team attempt to kill the titan below, with two being caught and another being knocked into a wall. Still in shock, Armin watches as his teammates are eaten or torn apart. A nearby titan, taking advantage of the trauma, grabs Armin and attempts to swallow him. Bleeding and half unconscious, Eren sees his friend in need and briefly remembers a childhood memory. Gathering all of his strength, he picks himself up and rushes to the aid of his friend. Inside the mouth of the titan, Eren grabs Armin before he's swallowed and throws him outside. With Armin now safe, Eren attempts to escape. As they reach for each other, the titan bites down and cuts off Erens arm, who is now trapped inside of its mouth. Armin watches in terror, as the the giant swallows Eren. In the distance, Mikasa is seen staring in the direction of her friends with an uneasy feeling.