Cheerful adolescent Karada Iokawa grows up under the care of her adoptive brother Hiro after being orphaned at two. Determined not to burden him, she cultivates self-reliance early, mastering cooking and household management despite her youth. Her petite frame and youthful demeanor invite others to infantilize her, fueling insecurities about her perceived immaturity, though she remains oblivious to Hiro’s lack of biological relation.

A shrine’s magic abruptly swaps her physique with that of Hiro’s ex-girlfriend Shouko, catapulting Karada into adulthood. Overnight, she faces logistical hurdles like forging identification and securing employment while masking her true identity. The dissonance between her adult appearance and unresolved adolescent emotions sparks an identity crisis, compelling her to confront the complexities of maturity.

Her classmate Tetsumasa, previously drawn to her child form, confesses feelings to her adult self, sparking a mutual romance. Their bond fractures when he manipulates her into a non-consensual act under warped romantic ideals, leaving lasting trauma. Tetsumasa later attempts atonement by seeking a wish to mend their fractured dynamic.

Struggling to reconcile her craving for autonomy with adulthood’s demands, Karada gradually shifts from rivalry to cooperative reliance with Shouko as both adapt to their reversed ages. Hiro’s protective role grows strained by guilt over past abandonment of Shouko and concealed truths about his non-biological ties to Karada, explored more deeply in the manga.

Official adaptations underscore her journey toward self-acceptance amid mounting responsibilities. The anime resolves with restored identities and reconciliation, while the manga expands the story with new contenders for the wish-granting stone and darker relational tensions. Both iterations emphasize her resilience in navigating adult challenges while clinging to vestiges of adolescence.