Heaven's Door starts off with rugged Katsuhito Aoyama (Tomoya Nagase) getting canned from his job as a car mechanic. While leaving work, he suffers from a migraine that causes him to nearly pass out. Katsuhito then visits the hospital to receive some ultra-heavy news: the cause of his migraines is an inoperable brain tumor the size of a human fist that will likely take his life in the next couple of days. During Katsuhito's first night at the hospital he meets a spunky girl young named Harumi Shiraishi (Mayuko Fukuda), who steals his cigarettes. Harumi is also a terminally ill patient suffering from cancer. Later that evening, the two sneak down into the cafeteria area and drink lots of tequila together. While in a drunken haze, Katsuhito decides to take Harumi out of the hospital and to see the ocean for the first time in her life. When the pair walk out of the hospital they spot an expensive import car with its doors unlocked. What Katsuhito and Harumi are unaware of is that the car has millions of dollars in its trunk and its owners will resort to any means to retrieve their money.