Silver-haired, blue-eyed Aruka has become a goddess, though she has little memory of her former human life and retains very human needs—chief among them, hunger. Unable to eat ordinary food, she sustains herself by secretly consuming the invisible monsters that cling to people, using a false fortune-telling act to find them. Her life of quiet, lonely feeding changes when she encounters Akira, a listless high school boy who has stopped attending school. Akira possesses a strong spiritual sensitivity and, due to his gloomy nature, passively attracts a steady stream of strange creatures, making him a highly convenient food source for Aruka. What begins as a purely transactional arrangement—Aruka eating the ghosts that plague Akira—slowly deepens into a peculiar, sincere friendship.

Aruka resides in the titular room 303, and the story follows her and Akira as they navigate a world where the supernatural is hidden just beneath the surface of everyday life. Akira’s withdrawn existence begins to change as he spends more time with the energetic and eccentric goddess. Their growing bond draws in other spiritually aware individuals: a classmate with a romanticized view of the occult who encounters a genuine urban legend, a delinquent student haunted by a different deity, and a former friend of Aruka’s from her past life who is now a determined spiritualist. These encounters force both protagonists to confront not only external supernatural threats but also the unresolved mystery of Aruka’s origin—namely, that she died by suicide seven years ago and became something that may not be a true god at all.

As the town becomes increasingly overrun by rampaging spirits and teeters on the edge of collapse, the only way to restore peace appears to be binding Aruka to the land as a properly enshrined deity. This would grant her stability but also tether her permanently, forcing Akira and Aruka to make a difficult choice about their future together. Their relationship evolves from a strange friendship into a deeper, more committed bond, with Aruka discovering a desire for a normal youth and Akira deciding to stand by her side no matter what. The narrative balances lighthearted, humorous moments of daily life with progressively darker revelations about the cost of divinity, the nature of monsters, and what it means to wish for happiness when one is no longer quite human.