Akira Tendo is a 24 year old office worker trapped in a soul crushing job at an exploitative company, where endless hours and harassment from his boss have left him feeling more dead than alive. He lives in a small, messy apartment in Tokyo, his days blurring together with no purpose or joy. Then a zombie apocalypse sweeps through the city. While everyone else flees in terror, Akira experiences an unexpected rush of relief: he never has to go to work again. For the first time in years, he feels truly alive.

Rather than focusing solely on survival, Akira creates a bucket list of one hundred things he wants to accomplish before he inevitably becomes a zombie himself. His first item is simple: drink beer all day. Other items include eating at expensive restaurants for free, going on a roller coaster, visiting a haunted house, meeting the woman of his dreams, and becoming a superhero. The zombie apocalypse becomes his unexpected vacation, and he approaches each day with manic enthusiasm.

Akira soon reconnects with Kencho, his college best friend and former rugby teammate who is now a real estate agent secretly dreaming of becoming a stand up comedian. Kencho is charismatic, promiscuous, and bulkier than Akira, but shares his friend's athletic background and newly awakened zest for life. Together they acquire an RV and begin traveling across zombie infested Japan, checking off bucket list items with chaotic energy.

Their journey brings them to Shizuka, a resourceful and pragmatic woman who previously worked as a flight attendant under the controlling thumb of her father. In the film, her character absorbs elements from a manga only character named Yukari. Shizuka is laser focused on survival, viewing Akira and Kencho's carefree attitude as reckless. However, she reluctantly joins them when she realizes she cannot drive the RV alone. Over time, her cold exterior begins to crack as she witnesses their genuine joy and friendship.

The group faces threats from both the undead and the living. They encounter Gonzou, Akira's sadistic former team leader from his old company, who has established himself as the tyrannical leader of a survivor camp at a truck stop. Gonzou traps passing travelers and forces them into labor, manipulating everyone around him with the same abusive tactics he used in the office. Akira nearly falls back into his old submissive mindset, but Shizuka helps him break free by writing walk out on Gonzou as an item on his bucket list.

The film compresses several arcs from the source material into a streamlined narrative. One major sequence takes place at a marine aquarium, where Akira dons a shark proof suit and embraces his childhood dream of becoming a superhero. This leads to a confrontation with zombie sharks and allows Akira to finally save people in the way he always imagined as a boy. In a significant change from the manga, the film merges the abusive boss arc with the aquarium setting, having Akira confront and ultimately rescue his former tormentor in a moment that defines what heroism means to him.

Other characters from the broader story, including Beatrix, a German Japanophile armed with samurai weapons, do not appear in the film adaptation. The film instead focuses tightly on Akira, Kencho, and Shizuka as they travel through a brightly colored, absurdist version of post apocalyptic Japan, where Akira discovers that even the end of the world cannot crush the human desire for joy, friendship, and purpose.