I Am a Hero [Manga]

Hideo Suzuki is a manga artist having a hard time getting his work published and it doesn’t help that his relationship with his girlfriend isn’t doing so well.
Sometimes he’ll have hallucinations and see and talk with a boy named Yajima or see faces outside his window or under his bed.
One night after work he was walking home and sees a pedestrian hit by a car and killed instantly. The pedestrian turns out not to be and despite having severe injuries and a twisted neck gets up and walks away. Upon seeing this Hideo isn’t sure if it was real or another one of his hallucinations. He sees even more strange things and just thinks he’s seeing things because of stress and work.
He wakes up in the morning and goes out to check on his girlfriend and when he arrives he finds her transformed into what seems to be a zombie like creature. He manages to kill her and escape and upon making it outside he realizes there are more of these out there and that their numbers are increasing.
He decides that he is going to be a hero that will survive this disaster and with his trusty shotgun sets out to survive in a terrible new world.