The Embroidered Door Echoes

A sophomore in high school found an ancient iron door while cleaning at school. After accidentally entering it, he actually traveled to a strange world. However, this world overlapped with the main world in some places. When he was about to accept the reality and live a good life in the new world, he accidentally contracted an incurable disease. It seemed to be related to which "door", and he could only find a way to survive if he found the door.