Aiko Morimura, 14, lives with her uncle, Mr. Fujinami, clinging to the belief that her father—missing since a vanished yacht voyage a decade ago—remains alive. Her mother, a hat designer in Paris, left Aiko in Japan, deepening her loneliness after the death of her dog Papi, a farewell gift from her mother before her own fatal car accident. This grief softens when she adopts Spank, a clumsy, cheerful stray whose loyalty and antics slowly mend her fractured heart.

Outgoing and vivacious, Aiko dreams of becoming a singer, often belting karaoke tunes with friends Shinako Yoshimura and Ryoichi Shinoda. Her affection for animals, especially dogs, clashes with Spank’s mischief, which disrupts her routines. Tensions flare with Serino Mihara, a wealthy classmate whose cat, Cat, becomes an unwitting rival as Spank develops a crush on the feline, sparking playful clashes.

Her life grows more complex with Rei, a beach-loving boy tied to Spank’s missing owner. Their connection mirrors her unresolved feelings about her father’s disappearance, though the manga reveals Rei’s accidental role in Papi’s death—a detail omitted in the anime. Aiko fiercely protects Spank from challenges like the aggressive cat Torakichi, their bond shifting from reluctant care to mutual dependence, reflecting her gradual acceptance of loss.

Divergent adaptations shape her journey: the manga keeps her mother in Japan, emphasizing familial bonds, while the anime’s Parisian separation highlights self-reliance. Both versions trace her path toward healing, fueled by unwavering hope in her father’s survival and Spank’s steadfast presence, culminating in resilience forged through love, loss, and newfound stability.