The protagonist, a salaryman exhausted from overtime, wakes up to find himself trapped in a dark, enclosed space that feels like a wooden box. He soon realizes he's not in a box but has hatched from a large, slimy egg. Looking at his reflection, he discovers he has been reincarnated as a dragon, with scaly, earth-colored limbs and claws.
Confused and disoriented, he finds himself in a desolate desert landscape resembling the Grand Canyon, under two suns. His immediate concern is hunger, and he discovers that he can eat the remnants of his eggshell, which tastes surprisingly like a snack. He then encounters black rocks that he finds inexplicably appetizing, consuming them voraciously. He notes that his new dragon body instinctively knows how to move on four legs and that his senses are heightened.
As he explores, he observes massive birds and other dragons flying in the sky, realizing he is in a different world, possibly not even Earth. He recalls a former colleague who was interested in fantasy novels, suspecting he might have been reincarnated into a similar "isekai" world. His primary goal becomes finding shelter, as he is vulnerable in the open.
He stumbles upon a colossal bird's nest atop a large rock. Investigating, he witnesses baby birds cruelly pushing their unhatched siblings out of the nest to their deaths. Despite the disturbing sight, the protagonist, now a dragon, views the fallen eggs as a protein-rich food source and consumes them with relish. He then encounters the massive parent bird, a terrifying creature that breathes fire, and quickly retreats.
Deciding he needs a safe haven, he resolves to dig his own shelter. He discovers that he can eat rocks and soil, which not only fills his stomach but also allows him to excavate. He begins digging a burrow, which he envisions as his "dream home." During this process, he experiences his first molt, shedding his skin and growing larger. He also discovers that different types of earth and stone have distinct flavors, with red stones and gems proving exceptionally delicious and invigorating.
While digging, he accidentally breathes fire, a "dragon's breath," which causes a large explosion. This attracts the attention of a massive dragon, which attacks him with its own breath weapon. The protagonist narrowly survives by being blown back into his partially constructed burrow, which collapses around him. He realizes the danger of his new world and decides to remain underground for safety and to continue growing. He dedicates himself to expanding his subterranean home, which he likens to an ant colony or mole's burrow, and finds a strange satisfaction in this solitary, earth-eating existence. He also discovers that he can sculpt stone and creates various statues, including one resembling a thousand-armed Kannon. He notes that his home is expanding deeper and deeper underground as he continues to eat and dig.
