The ending of The Great Flood reveals the entire film is a complex simulation, a test An-na designed herself. In the final moments, An-na breaks the time loop by finding her son, Ja-in, in a rooftop closet, proving that a synthetic mother’s love can be engineered to save humanity. This reunion, which occurs after 21,499 simulation cycles, fulfills the purpose of the “Emotion Engine” project and paves the way for the rebirth of the human race on a devastated Earth.
The Truth Behind the Flood and the Simulation
The first half of The Great Flood presents a straightforward disaster story. An-na, a researcher, and her young son Ja-in attempt to escape their flooding Seoul apartment building. They are aided by a mysterious man named Hee-jo, who tells An-na she is essential to humanity’s survival. The shocking twist is that the dramatic flood escape is not the core reality.
The truth is that the catastrophic global flood has already happened, wiping out most of humanity. An-na worked for Isabela Labs on a project called the Emotion Engine. With Earth doomed, scientists planned to repopulate the planet with synthetic humans. They could create synthetic children but could not give them genuine human emotions, nor could they create synthetic mothers with the innate instinct to care for a child.
An-na proposed a solution: create the children first, have them raised by human caretakers to develop emotions, and then design mothers whose core programming is the unconditional love for a specific child. To test this, she designed an extreme simulation. A mother would be placed in a repeated loop of her worst memory and would have to successfully find and save her child to prove her emotional capacity.
An-na and Ja-in’s Fate in Reality
In the actual events, An-na was forced to make a terrible choice. On the rooftop of the apartment building, soldiers took Ja-in from her. She was forced to leave him behind to board an evacuation helicopter. Before she left, she whispered a promise to him, telling him to hide in a closet on the rooftop next time.
Ja-in was killed so that the emotional data stored in his synthetic brain could be extracted for the Emotion Engine project. An-na was evacuated to a spaceship but was mortally wounded by debris during the journey. In her dying moments, she volunteered to be the first test subject for her own simulation, asking to become the synthetic mother for Ja-in.
Therefore, both An-na and Ja-in are physically dead. What we see for most of the film are digital constructs based on their downloaded memories, trapped in the endless simulation An-na designed.
Breaking the 21,499-Cycle Time Loop
Within the simulation, An-na is stuck in a time loop, reliving the day of the flood. Each day, she wakes up, tries to find Ja-in, and if she fails or dies, the day resets with her memories wiped. Over thousands of cycles, she begins to retain fragments of memory from previous loops. She uses this knowledge to change her actions, like saving a girl trapped in an elevator and helping a pregnant woman—experiences that help build the emotional range needed for the Engine.
A key clue comes from Ja-in’s drawings. An-na finds thousands of nearly identical pictures on her phone that he sent across different loops, all showing her by the helicopter. This confirms the repetitive nature of their reality. The number on An-na’s shirt in the final sequence reveals this is loop number 21,499, meaning she has been trying to find her son for the equivalent of nearly 59 years.
Guided by her growing memories and instinct, An-na eventually makes her way to the rooftop. She opens a closet door to find Ja-in, unmoving. She revives him with orange juice, and he wakes up and tells her, “You promised you’d come back for me”. He had been hiding there in every single loop, remembering the promise she made in real life. Their reunion, driven by a mother’s love and a child’s faith, finally breaks the simulation.
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The Ending’s Meaning and the Mid-Credits Scene
The successful reunion proves An-na’s Emotion Engine works. The synthetic mother’s love for her child has been fully realized, passing the test. The simulation ends, and the final shot shows a giant wave crashing over An-na and Ja-in as she tells him to hold his breath—symbolizing the end of their old cycle and a new beginning.
The crucial mid-credits scene shows what this success means for humanity’s future. We see multiple escape pods, or “capsules,” heading toward Earth. Inside one of them are An-na and Ja-in, now in new synthetic bodies, holding hands. They are not alone. The experiment’s success means the model can be replicated. Many mother-and-child pairs are being sent back to Earth to repopulate the planet, carrying with them the emotional bonds that define humanity.
The story of The Great Flood is ultimately one of hope and redemption. An-na, who failed to save Ja-in in reality, gets a limitless number of chances to fulfill her promise in the simulation. Her love, tested across thousands of lifetimes, becomes the very foundation for rebuilding a lost world.
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