Four years ago, a terrible tragedy shattered his life. Since that day, a teenage boy named Sunny has not left his house, becoming a complete shut-in living in the reclusive bubble of his home in the small, seemingly quiet town of Faraway. Hoping to give her son a fresh start, Sunny's mother decides the family will move away. With only three days left before they leave, there is a knock at the door. It is his childhood friend, Kel, who has come to reconnect after years of silence.

Reluctantly, Sunny steps outside for the first time and is thrust back into a world he no longer recognizes. His friends have all changed. The once sweet-natured Aubrey has become a bitter, pink-haired delinquent, while the gentle and photo-loving Basil is now consumed by a paralyzing fear. The group's reunion does not go well, reawakening a dark and painful past that Sunny has desperately tried to forget. As Sunny wanders the town with the ever-optimistic Kel, he finds himself unraveling the threads of a complicated history involving their departed friend, Hero, and the lingering, profound absence of his beloved older sister, Mari.

When the pain of the real world becomes too much, Sunny collapses into unconsciousness and retreats to a place called White Space. This is a stark, empty room that serves as the gateway to a vibrant, surreal dream world. In this realm, Sunny is replaced by his silent, emotionless alter-ego: Omori. Here, four years have not passed. The world is a colorful, whimsical RPG-like adventure land where all his friends are still young, happy, and together. Kel is energetic, Aubrey is kind, Basil is cheerful, and Hero is reliable—all presided over by the warm and gentle presence of Mari, who is very much alive. In this Headspace, Omori and his friends go on quests, fight goofy enemies, and eat infinite picnics, serving as a perfect escape from the guilt that plagues his reality.

The peace of Headspace begins to crack as Omori and his friends search for Basil, who has mysteriously vanished. Their journey to find him leads them through increasingly bizarre and unsettling environments. As they venture deeper, the cheerful facade of the dream world breaks down, revealing darker, corrupted spaces filled with monstrous creatures and unsettling truths. Meanwhile, in the real world, Sunny is forced to confront the fractured relationships with his old friends over the course of three days. The group must slowly piece together what really happened on the day of the recital four years ago, an event that led to Mari's death and ripped their friendship apart.

The narrative builds toward the inevitable collision of these two realities. As Sunny gets closer to the truth of the incident—involving a flight of stairs, a broken violin, and a cover-up—the dream world begins to fall apart. Omori, who exists specifically to repress this trauma, becomes hostile. The story leads to a final, climactic confrontation inside Sunny's mind where Omori tries to force him to succumb to despair and oblivion. Ultimately, Sunny must face the horrifying memory he has hidden from himself and decide if he can forgive himself for what he did, fighting for the chance to live in the real world and finally confess the truth to the friends he left behind.