Seiran, the eldest of seven children, works as a chore girl and part-time healer at her impoverished village church, supporting her sickly mother and siblings after their "scumbag" father abandoned them. Her meager healing abilities, limited to minor ailments, are barely enough to sustain her family. Their already dire situation escalates when a merchant arrives, demanding Seiran's youngest sister as payment for their father's debt. Desperate, Seiran tries to offer herself but is rejected. With only a month to pay an impossible sum, she seeks help from the village priest, who, unable to lend money, contacts the central church.
Days later, a strikingly handsome, high-ranking priest named Luca de la Rovere arrives from the central headquarters. He offers Seiran an astronomical sum for a job, enough to secure her family's future, provided she meets specific physical criteria (ash-grey hair, blue eyes, five feet tall, young female) and possesses a magical attribute. Seiran, fitting the description with her rare healing power, accepts despite her deep suspicions, sealing the contract with a blood oath.
Luca reveals the job: Seiran is to be a "stand-in" for the real Saintess. The current Saintess, a spoiled and selfish fifteen-year-old, married her attendant and fled on a honeymoon to avoid a mandatory pilgrimage across the country. This pilgrimage is crucial for the kingdom, which expanded through "holy wars" and forcibly converted conquered territories to Goddess Acera worship, leading to widespread resentment. The Saintess's tour is meant to enforce this conversion. Luca, aware of the real Saintess's escape, had been secretly searching for a decoy.
Seiran is rushed to join the pilgrimage team, which consists of the intimidating, red-haired Knight Commander Darren Ronheim, and the powerful but disrespectful twin mages, Faril and Will. All three harbor deep resentment towards the "Saintess" due to past humiliations by the real one. Seiran is confined to a prison-like carriage, her unease compounded by Darren's veiled threats. Luca, observing Seiran, finds her pragmatic worldview, shaped by poverty and a focus on survival and health, intriguing.
The first stop is a hostile village. Seiran is immediately pelted with raw eggs by two boys. Instead of reacting with distress, Seiran, enraged by the waste of precious food, apprehends the boys and delivers a furious lecture on the nutritional value of eggs and the importance of not wasting food. Darren, initially amused, is stunned by her unexpected reaction, which challenges his prejudices.
During the subsequent prayer ceremony, Seiran's heartfelt prayer triggers her "cleaning magic," purifying the dusty church with a visible light. The local priest is moved to tears, seeing it as a miracle. Darren, witnessing this, is completely convinced Seiran is the "true Saintess." Overwhelmed by guilt for his past disrespect, he prostrates himself, begging her to "step on him" as punishment, a request Seiran finds utterly bewildering.
Later, during a walkabout, more hostile villagers confront Seiran with eggs. Seiran again stops them from wasting food, challenging them to a "mud fight" instead. She recruits the egg-throwing boys (as punishment) and a guilt-ridden Darren to her team. The ensuing chaotic mud fight, which draws in more villagers, unexpectedly breaks the ice, replacing hostility with shared amusement. The villagers, initially suspicious of Seiran as a "church operative," apologize, surprised by her un-Saintess-like behavior.
That evening, Luca reveals the full extent of his "black plan." The pilgrimage is indeed dangerous, with potential for violence and assassination in these resistant territories. He admits he deliberately let the real Saintess escape because her spoiled nature and devoted entourage would have caused disaster or even massacre if she faced such hostility. Seiran realizes she was recruited as a disposable decoy for a life-threatening mission, a fact Luca casually reveals with a smile, confirming her initial suspicions about the "too-good-to-be-true" offer.
From a desperate village girl, Seiran has become a Saintess decoy navigating a dangerous political mission. Her pragmatic personality and unexpected actions have, against all odds, begun to disarm hostility and change perceptions, particularly Darren's. However, she now faces the full, life-threatening reality of her role and the manipulative nature of her employers.
