Giuseppina, a blue-green whale conjured by young Santiago's imagination, dwells nightly in a glass of water on his bedside table. Santiago alone typically sees or hears her, though his younger sister Rosa intermittently senses her presence.

She freely shifts her size—from mouse-small to mountain-large—and flies. Despite being imaginary, her interactions with the physical world yield real consequences, like seismic tremors when agitated.

Giuseppina mentors Santiago through childhood trials, offering emotional stability as he faces insecurities, complex family ties with his strict father and gentle grandmother, and social hurdles. Her guidance includes helping him mourn his grandmother’s death, supporting him during sacraments like his First Communion, counseling him on his changing relationship with Rosa, and fostering his confidence as he forms new bonds, particularly with a girl named Celia.

Her existence binds intrinsically to Santiago’s emotional needs. As he matures and gains self-reliance, his dependence on her fades, culminating in his outgrowing her companionship. The narrative implies a transition: Rosa’s recurring perception of Giuseppina suggests she may become Rosa’s companion after Santiago’s emotional departure.