Side story: Fight with titan monster

There is a city called clonium city. The people lived in the city in peace, but outside of the city there were monsters called titans. The monsters attacked the places to eat humans. This city was kept safe because of defensive system that surrounded the city. There were atomatic guns and electrocity devices. They kept the city safe from the titans. In this city, A boy lived. The boy's name was Ray Heller. He was a 16 year old normal boy that lived in town. He lived in a normal and cheerful life. But this is going to change now. One day he was walking on top of the wall that protected city with defensive system. He looked at far distant, when suddenly the wall begin to shake. He tried to catch something, but it was too late and he fell from top of the wall to outside of the city. When he fell, he saw something horrible. It was a titan. A titan was hitting the city wall. When it saw Ray-kun it roared and attacked him. Ray-kun runned. The titan attacked him with sharp claws and was able to hurt Ray-kun in his body with sharps leaving scars and blood coming out of them. The Ray-kun screamed in pain, but he didn't give up and runned again. His hand got damaged and got broken. Then Ray-kun runned and finally he found a safe place and got in there to hide. His body hurted and burned because of the damage titan did to him. He found some clothes and use them to close his wounds and put his hand in an unmoved state. Ray-kun said: Boku (I found a safe place, but how long can I stay here?) He thought if he just keep sitting and do nothing he will die. But he didn't wanted to die. He walked around there and found a sword. Due to the fact he could only one arm it was pretty hard to do it. But he started training with just his right arm and started getting stronger by training. After 3 days he finally got used to it and become stronger. Then he decided to leave and fight with titans. He started to move. When he got out of there 3 small titans attacked him. First a small attacked with it's claws. Ray-kun blocked it with his sword and then jumped and stuck the sword it titan's head. Then he jumped and cut another titan's head. He killed all 3 titans. Then he thought what should he do. He was both hungry and thirsty. He wanted to learn more about titans. He cut one titan's body and found a crystal inside it. He took it off titan's body. It said eat this and you will become stronger. Ray-kun didn't know if this was a joke or real. He decided he had nothing to lose and ate it. Then he started feel a strong pain in his body. Then he saw something, A memory. The memory showed this titan with other titans and were being talked by a human. The human talked that: I created you, all of you guys. So you will obey me. Here is your orders: You will attack humans and will kill all of them. When the memory was finished, Ray-kun opened the rest of titan's bodies and took off their crystals too. But he decided to do a research before eating them. He did his research in 2 days and then he left after eating them. When he moved to another place he saw the titan that had given him so much trouble. The titan saw him, but Ray-kun wasn't afraid. He was smiling fearlessly. The titan attacked him with it's claw, but Ray-kun just blocked it with his sword. The titan then tried to crush Ray-kun with it's feet, but Ray-kun moved fast and dodged it. Then he jumped and cut titan's feet. But that wounds regenerated. Then titan attacked with a fire breath. Ray-kun got hurt from that and fell to the ground. But he still was able to move. Then he attacked the titan. He cut it's foot, then jumped and cut it's arm, then he cut it's body. The titan was busy from regenerating, Ray-kun used that and jumped and put the sword in titan's head and cut it's mind. The titan finally died. Ray-kun cut it open and took the crystal. It was different than the little ones. He ate it, but he felt a very strong pain that was ten times stronger than when he ate the little ones. He took out something and drink it. After few minutes, the pain ended. Then he stood up and decided to try this new power. He breath out fire and it burned things around. Then he punched and broke somethings. He was ready to fight titans and the human who controlled them.