Boo is a young fairy living peacefully in the forest. He first appears as a child wearing simple natural attire: a green t-shirt and shorts woven from grass, a small hat made of grass blades, a golden pendant, and no shoes, carrying a tiny satchel. As he grows, his appearance matures: his hair lengthens, he wears a darker green jacket over his shirt, his shorts become longer pants with white trim, and his hat transforms into two distinct long leaves secured with leaf-like ties, visually marking his aging.

His constant companion is Mushiking, a legendary beetle inherited from his grandfather, serving as both protector and battle partner. Boo's tranquil forest life shatters when Adder, a banished fairy possessing magical abilities, arrives. Adder manipulates beetles through surgical modifications and a control whistle, unleashing aggressive foreign insects that threaten the ecosystem. Witnessing an attack, Boo and Mushiking confront Adder, revealing his motives: retaliation against the forest community for his expulsion and a desire to dominate the territory. Boo consistently opposes Adder's philosophy, declaring insects are friends, not servants, and the forest belongs to all equally.

Throughout the conflict, Boo displays bravery and strategic resourcefulness. He repeatedly intervenes to stop Adder's destructive plans, using his keen observation and insect knowledge to outwit foes. He physically tackles Adder to destroy his magic staff, preventing escape, and later confines him in a cage. Adder escapes by coercing a Mandibularis Stag-beetle into breaking the cage, injuring it. Showing compassion, Boo refuses the beetle's plea for euthanasia, instead summoning a Swallowtail Butterfly whose restorative scales heal it. This act earns the beetle's loyalty, helping Boo locate Adder's new hideout.

A pivotal confrontation sees Adder set fire to a tree, trapping Boo and the Mandibularis Stag-beetle inside. Forced to battle his former ally, Boo escapes the collapsing tree only to witness the forest ablaze. His despair turns to resolve when Mushiking arrives, revealing he has already alerted other forest dwellers to flee. Boo and Mushiking confront Adder at his fire-spewing stronghold, rallying rescued beetles against Adder's controlled minions. After defeating these forces, Mushiking sacrifices himself by tackling Adder into the flames, an event profoundly impacting Boo.

Boo's personality blends optimism, adventurousness, and a strong sense of responsibility. He thrives on new experiences and maintains hope in dire situations, sometimes avoiding negative emotions. His intelligence shines in creative problem-solving, like devising tactics during beetle battles or navigating hazards. Despite his youth, he prioritizes protecting others over personal safety, insisting on fighting Adder to save the forest rather than fleeing. This dedication occasionally leads to recklessness, such as pursuing Adder alone.

His character arc shows significant growth: he evolves from a carefree child into a determined guardian who understands the costs of leadership and loss. The forest's destruction and Mushiking's death deepen his resolve to uphold justice, cementing his role as a defender of the natural world.