Enjoy, fellow hybristophiliacs. This is not a super realistic description of insanity, and the feeling Eren feels in the beginning is sadism. That's how I experience it, anyway. It may be different for everyone, I don't know.
"That's it," Eren said, voice lost in the screams and whips of air of the Survey Corps as they flew by and were crushed by the titan.
He kneeled alone in the middle of the deserted and destroyed alleyway; no emotion showed on his face. Sweat was running down his face and body, mixing with the dirt stuck to him.
The lights in his eyes were gone, doused by the tears of the broken and battered. His mouth hung slightly open, his eyes almost shut. Exhaustion clouded his mind, along with something else he couldn't identify.
He struggled to swallow, finally managing it. "We're dead." His voice was monotone, but was shakily growing higher. "We're dead. The titans are going to kill us all. We're dead. There's no hope. We're all dead."
He snapped his head up, eyes glowing in something bone-chilling. Tears streamed down his face as he screamed in a high-pitched voice, "Why did we ever think there was ever hope for us!"
He stumbled up, grabbing his sword, and, with a burst of adrenaline, shot off into the air.
"Why, why, why, why, why!" he screamed as he saw Petra drop into a mouth with a scream and a fruitless struggle. "I know what I must do." His voice had dropped down to almost a whisper; his throat burned with the force of his screams from before. "I'll—I'll put you all out of your misery!" He screeched "misery" while he felt the wind whistling in his ears and blood pumping around his body.
He spotted Armin fighting against a titan in a ruined alleyway, watched him almost get crushed by its hand. Eren gritted his teeth, and pity for his friend swept across him.
I, a good friend, will make sure he won't die in such a horrible way as being eaten. I'm sure he'll go to Heaven. Too bad I won't see him anymore.
"E-Eren?" Armin had taken notice of his filthy and trembling best friend heading towards him. He was brought back to attention by the titan, who was swinging at him again with a huge hand. Armin growled and swung upwards, aiming his gear. He stabbed the titan in the neck and watched it collapse with a relieved sigh. He landed on the ground again, ready to fight.
A thud suddenly alerted him.
Eren had landed next to him on the ground. He turned to face him, smiling cheerily. "This is what good friends do, right Armin?"
Armin furrowed his eyebrows. "What do you—"
He never finished his sentence.
Eren screamed again and laughed and cried as he stabbed his sword right through his best friend's chest.
Armin, eyes wide and mouth open in a wheezing scream, could barely feel that his left lung was punctured; all he felt was immense pain. Eren pulled the sword out with a harsh yank. Blood instantly spread out from the wound and soaked the floor as Armin stumbled backwards and fell. Fingers grasped at his injury as he gasped for air.
Eren stared at his friend with pity and walked forward to him. He was grinning wildly, as if proud of himself.
Armin looked up at him, vision blurry, and struggled to say, "Why?"
"Why?" Eren knew what he was asking. "Why? Because we're all going to die and be eaten alive! Isn't this death better than slowly and painfully half-digesting in a stomach, then being vomited up?"
Armin's eyes filled with tears. He almost couldn't hear what Eren had said; he shakily and jerkily shook his head no. He struggled to pull in a breath, coughing when he breathed in his own blood. Blood splattered the floor and Eren's pants.
Eren glared at him. "Well, I'm sorry if you didn't die fast enough!"
He lifted the sword above his head with a frightening smile. Armin's eyes widened in terror.
"No, really; I'm really sorry. I enjoyed being your friend, though! You were just too weak in the end."
He thrust it down again into Armin's body, ripping open his heart. He died instantly, and the tears that were in his eyes trickled down his face. The water cut a clean line through the dirt and grime.
Eren simpered at his friend's corpse and leaped into the air, ready to continue his grim task.
I really like this! I will be continuing it when I'm the mood.