Light, a maiasaura, is the biological offspring of a mother who adopts an orphaned tyrannosaurus egg, nurturing its inhabitant, Heart, as her own. The family withdraws from their herd to raise the siblings in seclusion, shielding Heart from external threats. While Light and their mother sustain themselves on vegetation, Heart’s carnivorous instincts clash with their plant-based diet, his health declining as he resists his biological needs.

The siblings share an initially harmonious upbringing until Heart’s dependence on meat becomes undeniable, culminating in his awakening to his true tyrannosaurus nature. This truth fractures their bond, exposing the irreconcilable divide between herbivores and carnivores dictated by instinct and societal boundaries. Forced to confront his identity, Heart abandons the family to carve his own path, leaving Light and their mother to navigate life in his absence.