Third person POV

 "No…no…" a young man, a young half-Japanese, half-Spanish university student named Reina Taro, said with shock as he dropped his katana, "…what have I done?"

In front of him was a young scientist with dark grey hair and black eyes named Gen Yamashita, who was killed by Reina, and he is now on the floor of his zombie arena in his organization, Yami Kuro Yama.

The year was 2006 in the season of autumn.

The katana Reina just dropped from his hand was from Gen's.

Blood spilled from Gen's stab wound and onto the floor.

He is bleeding in his chest, but he is willing to die because of his evil deeds.

 "Thank you…" he uttered to Reina with a smile on his face, "…you had set me free from my darkness and sufferings."

He then closed his eyes and passed away.

 This causes Reina to realize what he has been doing. He thought that killing Gen would give him closure and vengeance for the death of his parents, but he realized that this act would only make things worse. He didn't feel closure, but rather, he felt extreme guilt and regret for his actions. He now felt that he had become like Gen: a murderous monster. He shouldn't have accepted Gen's request to kill him. But it's too late. Because of all that, Reina felt extremely guilty and fell on his knees crying and sobbing. Then, he sobbed as loud as he could. His cries resonate across the huge arena, which was used by Gen for bloody battles between survivors and his army of zombies.

 And then, someone came. 5 men, including Gen's head researcher and one of Gen's squad leaders, came rushing to the scene, only to see their leader dead and blood on Reina's clothes and face. It seems that they had heard Reina's cries. They asked him what had happened.

 "I…I killed him…" Reina responded while standing up and wiping his tears.

The 5 respondents were shocked to hear that.

They didn't expect that their leader had killed in the hands of someone else.

 "He told me to kill him…" Reina continued while sobbing his regrets away, "…I shouldn't have accepted it."

There was a very short silence between them.

 "Please…help him…" Reina begged them in despair, "…save him…please."

Feeling pity for him, 4 of the 5 men lifted and carried Gen's lifeless body away while the fifth one, who was one of Gen's armed men, called for emergency medical care for Gen.

As that happens, Reina couldn't help but be consumed by his guilt, remorse, and regret.

Slowly but surely, he will lose his will to live.

 Later, he and the 5 men took Gen to the headquarters' medical wing, which was located southeast of the zombie arena. There the medical staff began to work on saving Gen from death. The scene was very hectic, with Reina and the 5 men being told to wait outside of the emergency room as surgeons worked to save their leader. While the emergency surgery was ongoing, the 5 men were worried that their leader would not survive. Reina was worried, too, but being consumed by guilt, he turned around and left the medical wing. As he walks to the main headquarters, his guilt produces dark thoughts that tell him that he doesn't deserve to live. He tears up again while walking.

Shortly thereafter, he saw a room on the third floor whose door was unlocked and opened. So, he went inside, closed the door, and slumped against the wall, crying and sobbing his regrets and guilt away as those things started to eat him on the inside. It was now that he was depressed and traumatized by his brutal actions against Gen.