3721 Night

According to legend: after a person dies, the person's soul does not leave the world immediately. There is a 21-day gap between humans and ghosts to allow humans to adapt to life in the underworld. During these twenty-one days, the deceased can only communicate with other deceased people in the funeral home every night. After the twenty-one dark nights, people can be reincarnated and start a new life. (This book is also called "Three Seven")