Kyosei

Labeled as a delinquent and bad influence, high school student Kyosei Ichinose choose to stay out of the people around him, indulge himself to his headphones, pick fights against other people and stay alone. 

He was later famous for being a dangerous fellow that even his fellow students and his teachers feared him.

One day, everything is normal until the world is now in turmoil after the appearance of a mysterious disease that turns humans into mindless cannibals, infecting humans all around the country in an alarming state.

After receiving a distressed message from his former friend, he reluctantly returned only to find the school overrun by the dead. Armed with his house keys, a revolver and a duffel bag containing a few items to aid the rescue, he returned to the school without knowing why he still need to rescue a former friend.

Outbreak Chronicles: Dead Pandemic

(This is not a sidestory, this is also part of the main storyline as this kid is crucial to the story)

I woke up groggily on my makeshift bed. It's a very painful situation for me to get sick in this time. During the last run yesterday, the moment I returned, I think I caught a cold which caused my loss of energy and the will to move. Thankfully, I stock up enough medicine for normal colds in my stash, allowing me to recover. Although I still feel too groggy and felt too lazy to move, I can't depend on anyone else but myself.

Feeling my forehead, my fever already toned down a little bit but there is still a little bit of hotness in the surface. I don't have a thermometer with me so I can't exactly tell whether I still have fever or this is my normal temperature.

The Life of a Kid in a Deadly World