The first chapter in volume 14 of the Horror World of Junji Ito series, The Story of the Mysterious Tunnel.
A girl named Mami is in hospital where she is awaiting brain surgery. She claims that the personification of death has visited her and that she is going to die soon. She pleads with Dr. Kuroda to save her, but Kuroda believes she is delusional. The man who visited her is actually another patient, Tetsuro Mukoda.
Mukoda has horrific nightmares which, although lasting only one night, are the equivalent of a year or more in his dream. The doctors have no idea what to do with him, but each night, his dreams become one year longer. Over time, events that happened yesterday now seem like fifty years or more ago to him, and he begins talking as if he came from a different century. He ages to look like an extremely old man.
One day, Mukoda wakes up screaming for Mami. He says that she is his wife whom he met in the hospital and they have now been together for thousands of years. Kuroda realizes that Mukoda dreamed of her as his wife after he first saw her in her room. Mukoda calls for Mami and goes to her room, but she screams and declares that death has come back to get her. Kuroda is able to explain to Mukoda that his life with Mami was yet another dream.
Shortly after this, Mukoda records his longest dream yet. When dawn breaks his body shatters into a pile of crystals, his body having grown too old to keep pace with his dreams. Kuroda studies the crystals but can't find a link to Mukoda's condition. Mami begins to have "long dreams" like Mukoda and when questioned, Kuroda admits he administered parts of Mukoda's remains to her. He reasons that since she fears death and thus, nothingness, reaching a state of eternal dreaming will enable her spirit to live forever. He has become obsessed with his "research" and believes that eventually, all of humanity will want to enter the endless dream.