Illusia is the main protagonist who begins his journey as a newly hatched dragon egg with no memories of his past life as an ordinary Japanese person. From the moment of his reincarnation, he finds himself completely alone in a dangerous forest, abandoned without parents to protect him and facing a world where his initial form is considered weak and even delicious to predators. He is guided by a mysterious skill called the Voice of God, which manifests as a screen in his mind displaying his status and abilities, though this voice refuses to answer his deeper questions about the nature of the world or how he arrived there.

In terms of personality, Illusia is fundamentally a kind and well-meaning individual who strives to remain gentle despite the harsh realities of his new existence. He can be timid and occasionally makes poor decisions under pressure, but he consistently demonstrates heroic tendencies and a strong moral compass when faced with genuine crises. His defining trait is his refusal to abandon others in need, even when doing so puts his own life at tremendous risk. This is most clearly illustrated when he chooses to confront a massively powerful Rock Dragon to save Myria, a young girl who had shown him mercy, despite his survival instincts and the Voice of God urging him to flee.

Illusia's primary motivation throughout his journey is the desire for strength and companionship. He is driven by a deep loneliness, having been deprived of human interaction in his new form, and this loneliness pushes him to seek out others even when it is dangerous to do so. His encounter with human adventurers, which nearly ends in his death, stems directly from his longing for connection. After being saved by Myria, he becomes fiercely devoted to her protection and formulates a long-term goal of gaining enough power to safely reunite with her and communicate properly. The mysterious Voice of God also urges him to aim for the top and become the strongest, a directive he accepts as his overarching ambition.

Within the story, Illusia's role is that of a monster protagonist forced to navigate a world where his very existence is often seen as a threat or a commodity. His early struggles involve simple survival against creatures like Dark Worms, which are known as Egg Eaters, and learning to use his limited abilities creatively, such as using fall damage resistance to defeat a stronger enemy by luring it off a cliff. His decision to reveal himself to human adventurers marks a pivotal moment, as he mistakenly believes they might offer friendship, only to be attacked because Baby Dragons are considered a culinary delicacy. This event leads to his most significant relationship.

The most important relationship in Illusia's life is with Myria Milleania, the young adventurer who intervenes to save him. After her companions injure him, she uses her magic to heal his wounds, earning his eternal gratitude and loyalty. When her party is later decimated by a Rock Dragon, Illusia risks everything to rescue her, carrying her unconscious body through a wolf-infested forest to the edge of a human village. Though he is forced to retreat when the villagers attack him, mistaking him for a threat, his bond with Myria becomes the emotional core of his character development. It is Myria who eventually gives him his name, Illusia, which is derived from her favorite flower. He also maintains a complex relationship with the Voice of God, which serves as both a video game-like system interface and a mysterious entity that offers guidance and evolutionary choices, sometimes speaking outside its normal parameters to encourage him toward greatness.

Illusia undergoes significant development as he progresses through his evolutions. Starting as a powerless F-rank egg with minimal health points, his first major decision comes when he must choose between the safer Little Dragon path and the riskier Baby Dragon path that offers greater long-term potential. He chooses the latter after hearing a mysterious voice urge him to aim for the top. His most consequential evolution occurs when he reaches level twenty-five and is presented with multiple options. Initially repulsed by the Young Plague Dragon because it is described as an evil, disaster-spreading monster, he ultimately selects this path upon learning it will eventually unlock a human transformation ability. Viewing this as his only chance to safely converse with others and reunite with Myria, he vows to be a benevolent Plague Dragon who resists his darker nature. This evolution grants him terrifying abilities like a deadly miasma capable of wilting flowers and a Disease Breath that can inflict terminal illnesses, ironically making him a literal walking bioweapon even as he struggles to remain kind. He also earns a title called Itty Bitty Hero for saving Myria, which offers a path toward true hero status and helps him balance his darker Wrongdoer title, earned from leaving a trail of defeated monsters behind him.

Notable abilities that Illusia acquires include fire-based attacks such as Baby Breath and Dragon Punch, which he creatively uses to cook his food as well as combat enemies. He gains a Roll skill for mobility, fall damage resistance, and can eventually fly after evolving. His poison resistance is earned accidentally after surviving a brush with toxic mushrooms. As a Young Plague Dragon, he commands more sinister powers including venom fangs and paralysis attacks, though his most potent abilities are the passive release of a deadly miasma and an active Disease Breath that can spread terminal illness. He learns to use Rest, a basic healing spell, though his progress with healing magic is hampered by the Wrongdoer title he has acquired. Throughout his journey, Illusia demonstrates adaptability and a willingness to learn, whether mastering the art of cooking meat over his own flames or acquiring the Greek Language skill by listening to humans speak, allowing him to gradually understand those around him.