Bocchiman

One day, a hikikomori with the ability to see ghosts receives a text "Help me" from an anonymous source. Feelings of heroism coax him to venture out to the outside world. The only problem is, every human being on earth is already dead. He searches for survivors but all he finds are corpses and ghosts. He eventually stumbles upon the person that sent him the the message. It turned out to be the person responsible for him becoming a hikikomori in the first place. Unfortunately, she´s also dead, and has become a ghost. She tags along with the boy, as they brave this new world together.