As soon as Asriel saw the colossal titan he picked up Mikasa in a princess carry and rushed towards the river. He thought of killing off the titans but was worried about Mikasa. Even if he wants to send her off alone to the safe zone, she would protest and would want to come with him. Even if he has somehow gotten her to not follow him, he was worried that something unexpected would happen. So he prioritized her safety first and swore to himself that he would pay the titans back later on with interest. He could've used shadow clones jutsu but forgot it in the thick of it.
"Eru...that....that titan.....what....are you.." said Mikasa with her voice shaking from fear.
" We don't have time Mikasa! We have to get to one of the river barges that goes into Wall Rose. Soon that wall will break since that titan is huge, it's definitely capable of doing so!" interrupted Asriel as he ran. Mikasa nodded as a reply and held on tight to him with one hand while the other held her scarf tightly.
Right now people were all gawking in horror of the titan larger than the wall but the river barges will soon be filled with people so before that, he had to get a place on a river barge towards Wall Rose. He could easily kill Reiner and Bertholdt and even Annie but he wanted to witness the events that occurred in the series. He will stop them in the future but not now. Right now he was excited, he was excited that the world was finally starting. Besides, the people have become far too complacent with living in the walls that they think it's safe for them as long as they don't go out. This event would wake them up. As he ran towards the river barges, he felt a large quake and a huge sound coming from the wall.
*BOOOOM*
Debris and huge rocks came flying out from the now destroyed Outside Wall Gate of Wall Maria. People were crushed left and right by the rocks, not even people living inside houses were spared, some people who were closer to the impact were blown away from shock waves. While the rock indiscriminately crushes people, titans soon rush inside of the wall in hordes. The colossus titan was nowhere to be seen now. It's as if it just vanished into thin air. People were already in chaos when the rocks came but now seeing the titans coming in, all hell broke loose as people started losing their minds in fear. People started pushing, fighting, and killing each other that were in front of them to get away quickly from the titans.
Elderly people were left behind. Some children lost their parents in the chaos and were crying, not knowing what to do and just stood where they stand. The soldiers from Garrison Regiment were trying their best to help out those people and children while directing the rest of the populace towards the evacuation sites, which are the river barges and the Inner Wall Maria's Gate. Titans were eating people and soldiers from Garrison Regiment alike, the latter was too laid back during peaceful times that now when disaster finally struck, they didn't know what to do. They couldn't even kill a titan. Some brave soldiers managed to kill some titans but they too were soon caught and eaten quickly. All of them were lacking training and experience. None of them stood a chance. The whole district was soon bathed in blood and pieces of human flesh and limps.
Luckily Asriel and Mikasa lived near the Inner Wall of Wall Maria so they were far from the chaos. By the time he reached the river barge, he felt another quake and a loud sound.
*BAAAMMM*
The armored titan had destroyed the gate on the Inner Wall Maria, along with killing tons of people near the gate. Just like the colossus titan, it vanished as well after making the hole. Chaos once again spread throughout the populace as the people didn't know what to do anymore. The soldiers from the Garrison Regiment guided the remaining populace towards the river barges. There the soldiers started loading the populace starting with children and women first. Asriel and Mikasa got on the first barge as it was quickly filled up with people. The barge quickly left the district as it headed towards Wall Rose. Asriel looked around and he saw titans in the distance eating people and abnormal titans wreaking havoc.
Mikasa held on to his arm tightly the whole time they were together. Her body pressed up against his, his body warmth made her feel safe and that everything would be alright. He noticed Mikasa was shivering quite a bit so he brought her into his embrace as they slowly left Shiganshina District. After a while, he explored the barge and found Eren and Armin. They were happy to see Asriel and Mikasa made it out alive, they told him what happened to Eren's mother. Eren vows to kill every Titan in existence and that he wouldn't stop until they are all wiped out.
They finally arrived at the refugee camp where they were given rations and a place to sleep. As the days passed, more and more refugees started to come in. Soon the rations given out were becoming more and more insufficient and there was a food shortage until finally, the royal government assigned a mission in which twenty percent of the human population that remained after the fall of Wall Maria were sent out to reclaim the land. The royal government sent out 250,000 soldiers and civilians from Wall Maria back out to reclaim the lost lands from the titans, but what can civilians do against titans except become food for them.
As expected, it was a blood bath, of the 250,000 soldiers and civilians sent to reclaim Wall Maria, less than 200 made it back alive. All it did was just feed the titans instead. No land was reclaimed and the titans still roam free inside Wall Maria. Mikasa, Eren, and Armin have become ten years old while Asriel eleven years old. Eren received his titan powers not long after the fall of Wall Maria. As his father took him away from the camp to a secluded forest and injected him with the titan serum telling him to get to the basement in their house to learn the truth. Eren in his pure titan form ate his father, gaining his titan powers. Eren didn't remember all this later, as the titan fluid makes one forget memories. After returning back to human he found his father eaten, already forgotten that it was he who ate him. He ran away from the scene while crying. The soldiers later found him wandering around the forest and took him back to the camp. When the soldiers asked why he was wandering around in the forest alone, he didn't remember why.
They stayed in a landfill working on a farm waiting to reach the appropriate age to join the military. After two years, they begin their first day on the training grounds in the 104th Cadet Corps as commandant Keith Sadies grills the fresh recruits as part of their "Rite of Passage." During those two years Asriel, Eren, Mikasa, and Armin went through thick and thin watching each other's back and became close friends.