Tohru is a powerful dragon from the dragon realm dimension. Raised in the Chaos Faction to view humans as inferior, she fought against human armies and rival dragon factions. Centuries before the main events, a god's divine sword inflicted near-fatal wounds during battle. Left dying in the human world, she was discovered by Kobayashi, who drunkenly pulled the holy blade from her back. This act saved Tohru, sparking unwavering devotion and romantic love for Kobayashi. Accepting Kobayashi's shelter offer, she became a live-in maid, shapeshifting into human form while often keeping draconic horns and a tail for comfort at home.

In human guise, Tohru appears as a buxom young woman with blonde hair tipped reddish, red-orange slit-pupiled eyes, and a magically conjured maid outfit fashioned from her scales. Her true dragon form is a colossal green European dragon with black wings and a pale underbelly, dwarfing multi-story buildings. This form grants immense physical prowess: superhuman strength to crater earth with punches, extreme durability to withstand catastrophic battles, regenerative healing especially for her tail, and vast magic. Her abilities include flight, fire breath potent enough to scatter storm clouds, dimensional portal creation, perception-blocking invisibility, and clairvoyance. Her tail meat is toxic to humans, yet she persistently offers it regenerated to Kobayashi as a misguided token of affection.

Initially naive about human customs and hostile toward humanity, Tohru transforms under Kobayashi's influence into a cheerful, energetic protector, diligently managing household tasks while fiercely guarding Kobayashi and close companions. Her romantic pursuit of Kobayashi drives persistent affectionate advances, culminating in mutual acknowledgment in the manga. She forms a familial bond with exiled dragon Kanna, acting as her protective older sister. Relationships with other dragons reflect her complex past: fractured friendship with Elma over factional strife evolves into a heated rivalry softened by Kobayashi's mediation; camaraderie with Lucoa and Fafnir contrasts with adversarial tension toward her father, Damocles, who opposes her human life and provokes confrontations halted by Kobayashi's defense of Tohru's autonomy.

Tohru's evolution centers on rejecting ingrained draconic hatred to embrace peace and domesticity. She prioritizes her chosen family with Kobayashi and Kanna over her heritage, willingly remaining in the human world despite outliving loved ones. This journey involves reconciling her chaotic nature with human norms, tempering protective instincts, and navigating conflicts among humans and dragons.