Satoko Houjou endured a traumatic childhood shaped by family instability and abuse. Her mother's multiple marriages led Satoko to use the surnames Hatake, Yoshizawa, Matsūra, and finally Hōjō. Distrusting her stepfathers, she perceived their discipline as abusive. Her parents' support for the Hinamizawa Dam Project made the family targets of village hostility, contributing to Satoko developing Hinamizawa Syndrome, a condition inducing severe paranoia and hallucinations. During a 1980 trip to Shirakawa Park, consumed by self-defense delusions, she pushed her parents off a cliff, causing their deaths. An alternate account suggests the deaths were accidental, caused by corroded railings when she rushed to embrace them during reconciliation.

Hospitalized at Irie Clinic, she nearly underwent vivisection as a terminal Hinamizawa Syndrome research subject. Dr. Irie's experimental drug C-103 saved her, requiring ongoing injections for stability. Afterwards, she and her brother Satoshi lived with abusive relatives, Teppei and Tamae Hōjō. Satoshi murdered Tamae to protect Satoko and subsequently vanished. Satoko then moved in with her orphaned friend Rika Furude.

Despite her past, Satoko typically exhibits an energetic and mischievous personality. She is renowned for crafting elaborate traps, often targeting Keiichi Maebara as pranks, though these prove lethally effective against threats. She possesses sharp analytical skills, evident when deducing bomb locations and school layouts during crises. Her speech features distinctive verbal tics, ending sentences with "wa" and using a unique "Ohoho!" laugh. She struggles to distinguish broccoli from cauliflower, suggesting possible color blindness, and intensely dislikes pumpkins.

She forms deep familial bonds. Originally dependent on her brother Satoshi, whom she affectionately called "Nii-nii," she later transferred this term to Keiichi, viewing him as a brother figure. She also called Shion Sonozaki "Nee-nee" (big sister), notably during Shion's sacrifice. Her closest relationship was with Rika Furude, with whom she lived and shared daily life. However, this bond fractured severely after Matsuribayashi-hen. When Rika decided to attend St. Lucia Academy outside Hinamizawa, Satoko struggled academically and socially in the strict environment, feeling abandoned. This led her to encounter the entity Eua at the Saiguden shrine. Eua granted her power to loop through time fragments, akin to Rika's ability. Determined to keep Rika in Hinamizawa forever, Satoko initiated new loops, orchestrating events leading to repeated tragedies and murder-suicides to reset time whenever Rika neared escape. During these loops, a distinct "witch" persona emerged, characterized by ruthlessness, manipulation, and willingness to kill allies like a reformed Teppei or her own conflicted human self. Her eyes occasionally glowed red in these states.

In the "perfect world" of Saikoroshi-hen, where no tragedies occurred, Satoko's personality diverged significantly. Living stably with her parents and Satoshi, she spoke formally and exhibited coldness towards Rika, resenting her perceived selfishness. This version is separate from the main timeline's Satoko. Decades later, in the Rei manga, she married Kisaku Kimiyoshi, ran the "Smile Store" souvenir shop in Hinamizawa, and had a daughter named Sakiko.

Physically, Satoko is petite with short blonde hair, often secured by a black headband. She has sharp canine teeth and reddish-violet eyes. Her typical attire includes a green school uniform with a yellow tie and black leggings, or casual pink shirts with denim shorts. When looping, her eyes sometimes took on a blazing red hue.